‘Will Work for Food’ – Extrafloral Nectaries

Wild Senna (Senna hebecarpa, S. marylandica) has so many stories to tell!  This tall, herbaceous plant has flowers that are unusual for a member of the Pea (Fabaceae) family.  Rather than curling to form the banner, wings and keel that are common Pea family characteristics,

Everlasting Pea (Lathyrus latifolius) with skipper

Everlasting Pea (Lathyrus latifolius) with skipper

Wild Senna’s petals are open and distinct.

Wild Senna (Senna hebecarpa) with Bumble Bee. Note the pollen on her rear legs.

Wild Senna (Senna hebecarpa) with Bumble Bee. Note the pollen on her rear legs.

Wild Senna’s flowers have another somewhat unusual feature, or more accurately, they lack a feature, nectaries, that many flowers have.  Many plant species have evolved to entice pollinators to their flowers by providing a reward of nectar in exchange for their visits. In spite of the lack of nectar, Wild Senna is pollinated by bees, primarily Bumble Bees but also Sweat Bees (Halictid species).  They visit the flowers for their pollen, a highly nutritious food that contains protein, carbohydrates, fats, vitamins and minerals; plenty of incentive for a bee to visit even without nectar.  Alerted to the possibility of food by the colorful yellow flowers, the adult bees come to dine on pollen and to harvest some to bring back to their nests for their larvae.

Many plant species have evolved to produce chemical compounds whose primary purpose is to protect the plant from being eaten by making it bitter, distasteful or even toxic to potential consumers.  Wild Senna is a species that has adapted to use this defense.  Both the leaves and fruits (seed pods) contain anthraquinones, which are powerful laxatives.  Often people take advantage of the protective chemicals that plants produce by finding medicinal uses for them. In the case of the Senna species, the laxative is used for treating constipation.

These chemicals are a very effective deterrent to many animal species that eat plants (herbivores).  Even in areas where there is severe deer pressure, it’s unusual to see Wild Senna browsed.  But this strategy is not effective against all potential herbivores.  There are some butterflies and moths, including the Cloudless Sulphur,

Cloudless Sulphur caterpillar on Wild Senna (Senna hebecarpa)

Cloudless Sulphur caterpillar on Wild Senna (Senna hebecarpa)

Sleepy Orange,

Sleepy Orange butterfly

Sleepy Orange butterfly

and the Common Tan Wave, whose caterpillars are able to eat the leaves or other parts of Wild Senna.  These insects have evolved to specialize on these and other closely related plants, without being harmed by the chemicals that are toxic to other species.

Which brings us to an interesting back-up strategy Wild Senna employs for protection.  Wild Senna has extrafloral nectaries, a nectar source separate from the flowers. They are positioned on the leaf petioles (stems) near their attachment to the primary plant stem and adjacent to the flower buds.  Why would a plant species offer nectar if it’s not a lure for pollinators?  It takes energy and resources to produce nectar.  What’s in it for the plant to provide this service?  Who feeds here?

The egg-shaped bump is an extrafloral nectary on a leaf stem of Wild Senna (Senna hebecarpa)

The egg-shaped bump is an extrafloral nectary on a leaf stem of Wild Senna (Senna hebecarpa)

Wild Senna’s extrafloral nectaries attract a variety of visitors, many of them beneficial members of the ecosystem.  The Sweat Bee below may have stopped here before or after visiting Wild Senna flowers for their pollen.

Sweat Bee feeding at an extrafloral nectary on Wild Senna (Senna hebecarpa)

Sweat Bee feeding at an extrafloral nectary on Wild Senna (Senna hebecarpa)

Many lady beetle species, including the Seven-spotted Lady Beetle pictured here, help to keep the aphid population in check.

Seven-spotted Lady Beetle feeding at an extrafloral nectary on Wild Senna (Senna hebecarpa)

Seven-spotted Lady Beetle feeding at an extrafloral nectary on Wild Senna (Senna hebecarpa)

This jewel-like creature is a Perilampid wasp, one of several parasitic wasps that specialize on various insect species as their prey, including some other parasitites.

Perilampid wasp feeding at an extrafloral nectary on Wild Senna (Senna hebecarpa)

Perilampid wasp feeding at an extrafloral nectary on Wild Senna (Senna hebecarpa)

For Wild Senna, ants are probably the most beneficial visitor to this nutritious food source.

Ant feeding at an extrafloral nectary on Wild Senna (Senna hebecarpa)

Ant feeding at an extrafloral nectary on Wild Senna (Senna hebecarpa)

Sugary substances like nectar are important food for ants.  But protein and other nutrients available from insects (including caterpillars) are also an essential part of the diet of most ant species.  Ants that are enticed to visit Wild Senna for its nectar can also hunt for and eat the insects that may be consuming the leaves or buds of the plant.  The placement of the nectaries between the leaf blade and flower buds is an advantageous location for protecting both plant parts.

Ant with caterpillar prey

Ant with caterpillar prey

You might think of the ants as an army of mercenaries paid in nectar to guard the plant, with as many caterpillars and other herbivores as they can catch as a bonus.  Ants will work for food!

Related Posts

Sleepy Orange Butterflies Overwintering in Pennsylvania

Cloudless Sulphurs are on the Move

Resources

USDA NRCS Plant Database http://www.plants.usda.gov/factsheet/pdf/fs_sehe3.pdf

Illinois Wildflowers http://www.illinoiswildflowers.info/savanna/plants/wild_senna.htm

Marshall, Stephen A.  Insects Their Natural History and Diversity.  2006.

Waldbauer, Gilbert.  What Good Are Bugs?.  2003.

Sleepy Orange Butterflies Overwintering in Pennsylvania

As I write this, it’s 30°F and snowing lightly, with snow, ice and rain predicted for the next few days.  It’s December in New Jersey.  Oddly, I like winter.  So what am I doing thinking about butterflies?

Sleepy Orange Nectaring on Pickerelweed (Pontederia cordata)

Sleepy Orange Nectaring on Pickerelweed (Pontederia cordata)

Since summer I’ve been puzzling over the fact that a butterfly species that is primarily tropical, the Sleepy Orange (Eurema nicippe or Abaeis Nicippe), has been seen regularly in summer across the Delaware River at Bowman’s Hill Wildflower Preserve, just south of New Hope, Pennsylvania.  (See Sleepy Orange Butterflies are Back)  This species is not thought to overwinter farther north than North Carolina.  How is it that Sleepy Oranges have consistently been at the Preserve for the past four summers, and before that in 2006 and 2008?

Is it random chance?  Are they successfully overwintering here?  Or have they evolved to be able to migrate south in the fall and back north in the summer, returning to the same location?  Inquiring minds want to know (ok, I want to know), so I gave myself the assignment of observing them throughout the fall to see if I could learn anything that could help answer this question.

Throughout August the Sleepy Oranges could be seen mating, with the females taking the lead in selecting the location, usually on or near their favorite caterpillar food plant, Wild Senna (Senna hebecarpa).

Sleepy Oranges mating on Wild Senna

Sleepy Oranges mating on Wild Senna

Naturally, this activity was followed by the females laying eggs.

Sleepy Orange laying an egg (ovipositing)

Sleepy Orange laying an egg (ovipositing)

Their efforts were pretty successful, treating me to many caterpillar

Sleepy Orange Caterpillar

Sleepy Orange Caterpillar

and chrysalis sightings throughout September.

Sleepy Orange Chrysalis

Sleepy Orange Chrysalis

Empty Sleepy Orange Chrysalis - the butterfly has already emerged

Empty Sleepy Orange Chrysalis – the butterfly has already emerged

The chrysalises masqueraded perfectly as leaflets loosing their chlorophyll and changing to shades of tan, yellow and orange.

By late September, I still saw fresh-looking adult butterflies in their summer coloration form.

Sleepy Orange, summer color form

Sleepy Orange, summer color form

In the south, where Sleepy Oranges are known to overwinter as adults in reproductive diapause, they have a different, darker coloration for this overwintering generation. I observed my first individual with this coloration at the Preserve on September 24.

Sleepy Orange, winter color form

Sleepy Orange, winter color form

This butterfly had just emerged from its chrysalis.  The tan leaf-like thing hanging behind and between the two leaves to the right of this butterfly is the recently vacated chrysalis, positioned perfectly as if it were a leaflet.

Empty Sleepy Orange Chrysalis

Empty Sleepy Orange Chrysalis

Throughout October, every time I looked on a warm enough day I eventually saw adult Sleepy Oranges.  They usually made their appearance by flying up from the ground, first one butterfly, then two, maybe three or four, flying constantly, circling around each other, flitting back and forth, until they disappeared back down to the grasses and fallen leaves on the ground.  I no longer saw mating, caterpillars or chrysalises.

Occasionally a Sleepy Orange basked from a tree branch, safe in the camouflage of the changing fall leaves.

Sleepy Orange basking on Willow Oak - Can you see the butterfly?

Sleepy Orange basking on Willow Oak – Can you see the butterfly?

Only very rarely did I see them nectaring, although they may have been feeding more than I was able to observe, possibly on blossoms of young plants at nearly ground level, like this aster.

Sleepy Orange nectaring on aster

Sleepy Orange nectaring on aster

The spot where I saw the butterflies most frequently is a small meadow area with lots of young plants (including Wild Senna, their caterpillar food plant) and exposure to afternoon sun.

My last sighting of an adult was on November 2, a mild sunny day with a high in the mid-60s.  Given the current temperatures, I’m pretty sure that will be my last sighting until next year.

So it appears that the Sleepy Oranges are at least attempting to overwinter here, probably as adults, and probably in the shelter of the plants and fallen leaves on the ground.  Lets see if they’re successful.  This fall and winter is starting out a bit colder than normal, so even if they have survived the winter here in the past, it doesn’t necessarily mean they’ll make it this year.  I hope they do!

Even if they do overwinter here, it doesn’t exclude the possibility that they might also have a second strategy that involves migration.

I’ll keep you posted.

Sleepy Orange, winter form

Sleepy Orange, winter form

Resources:

Cech, Rick; Tudor, Guy.  Butterflies of the East Coast.  2005.

Cloudless Sulphurs Are on the Move

Very common in the southern United States and Mexico, Cloudless Sulphur butterflies (Phoebis sennae) are much more rare in the northern states and Canada, at least until late in the summer when some individuals pursue their annual dispersal … north?  For the past few weeks I’ve been seeing them at Bowman’s Hill Wildflower Preserve, near New Hope, in the central part of eastern Pennsylvania.

Cloudless Sulphur on Wild Senna (Senna hebecarpa)

Cloudless Sulphur on Wild Senna (Senna hebecarpa)

Look for them flying rapidly while cruising for mates, hunting for caterpillar food plants and laying eggs, or nectaring.  The butterflies I’ve seen have been so busy with the first two activities that I haven’t seen much nectaring.

Cloudless Sulphur laying egg, or ovipositing, on Wild Senna (Senna hebecarpa)

Cloudless Sulphur laying egg, or ovipositing, on Wild Senna (Senna hebecarpa)

Cloudless Sulphur egg on Wild Senna (Senna hebecarpa)

Cloudless Sulphur egg on Wild Senna (Senna hebecarpa)

Cloudless Sulphurs specialize on pea family members, primarily Sennas and closely related plants like Partridge Pea (Chamaecrista fasciculata) and Wild Sensitive-plant (C. nictitans) as food plants for their caterpillars.  At Bowman’s Hill Wildflower Preserve the Cloudless Sulphurs seem to prefer Wild Senna (Senna hebecarpa, S. marilandica). Partridge Pea is also available here, although not as plentiful, but I haven’t yet seen them use it as a caterpillar food plant.

Cloudless Sulphur caterpillar on Wild Senna (Senna hebecarpa)

Cloudless Sulphur caterpillar on Wild Senna (Senna hebecarpa)

The caterpillars’ coloration blends perfectly with their food plants, varying from yellow to green.  At this location, their overall green background is an exact match for the color of the Wild Senna leaves on which they’re feeding.  The yellow stripe along the length of the caterpillar’s body resembles the leaf mid-rib, where they can be seen resting or feeding.  This camouflage makes it much harder for a hungry bird to spot them!

Wild Senna (Senna hebecarpa)

Wild Senna (Senna hebecarpa)

The caterpillars may eat the entire compound leaf, including mid-rib

Cloudless Sulphur caterpillar eating leaf midrib of Wild Senna (Senna hebecarpa)

Cloudless Sulphur caterpillar eating leaf midrib of Wild Senna (Senna hebecarpa)

and leaflets.

Cloudless Sulphur caterpillar eating leaflet of Wild Senna (Senna hebecarpa)

Cloudless Sulphur caterpillar eating leaflet of Wild Senna (Senna hebecarpa)

At Bowman’s Hill Wildflower Preserve they are sharing a habitat with Sleepy Orange butterflies, who are usually resident here from July through September, nectaring on a broad variety of flowers, mating, and laying eggs.

Sleepy Orange butterflies, mating

Sleepy Orange butterflies, mating

In the photo below, a Cloudless Sulphur is laying an egg directly opposite a leaf where a Sleepy Orange caterpillar is hiding.

Cloudless Sulphur on Wild Senna (Senna hebecarpa) laying egg opposite leaf where a Sleepy Orange caterpillar is hiding

Cloudless Sulphur on Wild Senna (Senna hebecarpa) laying egg opposite leaf where a Sleepy Orange caterpillar is hiding

These two butterfly species have a lot in common.  Sleepy Oranges use the same food plants for their caterpillars, and I have so far seen the same preference for Wild Senna rather than Partridge Pea at this location.  Both Cloudless Sulphurs and Sleepy Oranges seem to prefer using younger plants as caterpillar host plants.

Like Sleepy Oranges, Cloudless Sulphurs are primarily a tropical species.  Their range goes as far south as Argentina. In the moderate temperatures of a southern winter, they survive as adults, mostly inactive, but feeding occasionally.  They are somewhat cold tolerant, flying in fairly cool temperatures for butterflies.

But these bright, sprightly butterflies have an adventurer’s genes.  Most years, some individuals move northward, sometimes reaching as far as Ontario province in Canada, in spite of the fact that they can’t currently survive sustained cold winter temperatures. At least, as far as we know, they can’t.

So why do Cloudless Sulphurs keep pushing north every year if they can’t survive sustained periods of cold winter weather?  How is this beneficial to the species’ continued existence?

A species that can subsist over a broad geographic range in diverse habitats is in a better position to survive over time than one that is more narrowly focused.  If something happens to make one part of the range or habitat inhospitable, the species has many other options for locations that will accommodate their continued existance. The larger a species’ population becomes, and the more diverse the environments to which segments of the population are exposed, the more genetic mutations will result in individuals.  If the same genetic mutation occurs frequently enough, it may lead to an evolutionary change in the species.

Cloudless Sulphur laying egg on Wild Senna (Senna hebecarpa)

Cloudless Sulphur laying egg on Wild Senna (Senna hebecarpa)

Cloudless Sulphurs have evolved so that many of those that head north (or their offspring) make a return southward fall migration, spending the winter in a warm southern climate.

But some Cloudless Sulphurs continue to move north in late summer and fall, and probably die when the cold winter sets in.  But two things could happen to make this exploration of new territory a worthwhile effort for the species.  Warming temperatures could eventually make some of this northern territory moderate enough for the Cloudless Sulphurs to survive the winters as they do in the south.  Or a genetic mutation could occur in the Cloudless Sulphurs that leads to an evolutionary change, enabling them to survive a cold northern winter.  Their caterpillar food plants, Wild Sennas, are available to support them as far north as Ontario and all of the northeastern United States.

Cloudless Sulphur laying egg on Wild Senna (Senna hebecarpa)

Cloudless Sulphur laying egg on Wild Senna (Senna hebecarpa)

Resources:

Cech, Rick; Tudor, Guy. Butterflies of the East Coast. 2005.

Glassberg, Jeffrey. Butterflies through Binoculars A Field Guide to Butterflies in the Boston-New York-Washington Region. 1993.

Scott, James A. The Butterflies of North America. 1986.

Wilson, Edward O.  The Social Conquest of Earth.  2013

Butterflies and Moths of North America

Canadian Biodiversity Information Facility

Georgia Department of Natural Resources Wildlife Resources Division

USDA Plants Database

Sleepy Orange Butterflies are Back

Sleepy Orange butterflies are back at Bowman’s Hill Wildflower Preserve!

Sleepy Orange butterflies on Purple Coneflower (Echinacea purpurea)

Sleepy Orange butterflies on Purple Coneflower (Echinacea purpurea)

Sleepy Orange (Eurema nicippe) butterflies are a tropical species, present year-round from Central America through the southern tier of the United States. They may breed as far north as the southern tip of New Jersey, west to eastern Colorado, then dipping south to near Las Vegas, Nevada, but they are less common in the northern part of their range, and they are not thought to be able to survive the winter much farther north than North Carolina. Sleepy Orange is a species that likes to push the envelope of its territory, with individuals migrating each year to repopulate the northern areas.

So it’s pretty exciting to have Sleepy Oranges at Bowman’s Hill Wildflower Preserve, because it’s considered a rare ‘stray’ in Pennsylvania where the Preserve is located. It’s rare across the Delaware River in much of New Jersey, too. In 2012, ours was the only count circle in Pennsylvania or New Jersey to report Sleepy Oranges in the July 4th North American Butterfly Association Butterfly Count.

Even better, I have seen Sleepy Oranges at Bowman’s Hill Wildflower Preserve in 2006, 2008, and every year from 2010 through 2013, usually from July through September. Yesterday I counted 10 individuals.

What brings them to the Preserve? Likely it’s the reliable presence of one of their favored caterpillar food plants, Wild Senna (Senna hebecarpa).

Wild Senna (Senna hebecarpa)

Wild Senna (Senna hebecarpa)

Wild Senna (Senna hebecarpa) flowers

Wild Senna (Senna hebecarpa) flowers

Only the presence of this food source has made it possible for Sleepy Oranges to breed at the Preserve. Sleepy Oranges also use other plants in this genus, and Partridge Pea (Chamaecrista fasciculata) and Wild Sensitive Plant (Chamaecrista nictitans) as food plants for their caterpillars. These plants are all pea family members, and contain alkaloids, chemicals that may have a bitter taste to some predators. Sennas also contain another chemical that has laxative properties. It is probable that Sleepy Oranges evolved to specialize on these plants because the chemicals they obtain from this diet offers some protection against predators.

Sleepy Oranges Mating

Sleepy Oranges Mating

There are also plenty of nectar sources at the Preserve for the adult Sleepy Oranges, who are pretty eclectic in their tastes.

Female Sleepy Orange  on Tall Tickseed (Coreopsis triptera), 2013

Female Sleepy Orange on Tall Tickseed (Coreopsis triptera), 2013

Sleepy Orange nectaring on Wild Bergamot (Monarda fistulosa), 2008

Sleepy Orange nectaring on Wild Bergamot (Monarda fistulosa), 2008

Sleepy Orange nectaring on Heal-all (Prunella vulgaris), 2011

Sleepy Orange nectaring on Heal-all (Prunella vulgaris), 2011

Sleepy Orange nectaring on Cardinal-flower (Lobelia cardinalis), 2012

Sleepy Orange nectaring on Cardinal-flower (Lobelia cardinalis), 2012

Males are also known to dine on minerals, although I usually see them drinking nectar.

Sleepy Orange on Field Thistle (Cirsium discolor), 2006

Sleepy Orange on Field Thistle (Cirsium discolor), 2006

Wondering about this butterfly’s name? It’s not based on behavior, because this sprightly butterfly is very active. The photo below illustrates the characteristics that explain the origin of the name ‘Sleepy Orange’. The curved pattern of dark dots near the center of the upper edge of the forewing are thought to resemble a closed eye, resulting in ‘sleepy’, and the bright orange color, especially coming from the top (dorsal) side of the wing explains the rest. Sleepy Oranges overwinter as adults in the south; their winter color form is a darker red-orange.

Sleepy Orange nectaring on New York Ironweed (Vernonia noveboracensis), 2010

Sleepy Orange nectaring on New York Ironweed (Vernonia noveboracensis), 2010

Given the rarity of this butterfly species in the surrounding area, I can’t help but wonder how Sleepy Oranges have been consistently finding Bowman’s Hill Wildflower Preserve for the past several years. It seems unlikely that this primarily tropical species would be able to survive the winter here, but with warmer winter temperatures, who knows? There are some reports of a southern migration of these butterflies in the fall. Could some of the Preserve’s butterflies have flown far enough south to successfully overwinter, and genetically pass on the knowledge of this location to their offspring? Does the generation that overwinters as adults live long enough to make a return northward migration the following year? Is this location near the Delaware River just a favored migration route for Sleepy Oranges and once they see the food available here they decide to stay? Random chance?

If you have an explanation or theory for their consistent appearance here, I would love to hear it!

Female Sleepy Orange on her caterpillar food plant, Wild Senna (Senna hebecarpa), 2013

Female Sleepy Orange on her caterpillar food plant, Wild Senna (Senna hebecarpa), 2013

For more on Sleepy Oranges at Bowman’s Hill Wildflower Preserve, click Sleepy Oranges Overwintering in Pennsylvania.

Resources:

Brock, Jim P.; Kauffman, Ken. Kaufman Field Guide to Butterflies of North America. 2003.

Capon, Brian. Botany for Gardeners. 2005

Cech, Rick; Tudor, Guy. Butterflies of the East Coast. 2005.

Glassberg, Jeffrey. A Swift Guide to Butterflies of North America. 2012.

Glassberg, Jeffrey. Butterflies through Binoculars A Field Guide to Butterflies in the Boston-New York-Washington Region. 1993.

http://www.butterfliesandmoths.org/species/Abaeis-nicippe

http://www.gardenswithwings.com/facts-info/a0810MonarchMigration.html

http://www.learner.org/jnorth/tm/monarch/OtherMigrants.html