A carnivorous caterpillar in our backyard

It is easy to think that for fabulous, bite-you-in-the-nose, natural history, you have to go to the tropics. Not true! As a response to the covid pandemic, so many of us are spending more time outside in gardens and neighborhood parks. I have been posting (mostly on twitter, @anuragasclepias) some finds such as these two organisms below in and around Ithaca

1 tree hopper, probably a species of Publilia on Bidens frondosa
A tree hopper, probably a species of Publilia on Bidens frondosa
2 A wonderful late summer wetland plant, turtlehead (Chelone glabra, from the Plantaginaceae)
A wonderful late summer wetland plant, turtlehead (Chelone glabra, from the Plantaginaceae), which hosts the Baltimore Checkerspot butterfly, Euphydryas phaeton

Yet, I stumbled on the most spectacular find of the season when I was out with my Field Ecology class at Cornell last week. Now in the second week of classes, this is one of the few “in person” courses being offered in Ecology and Evolution this semester. Lucky for me, I am the instructor and the class revolves around a 4-hour field exercise every Friday

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Alder reproductive parts, female on the left and male on the right

Last week, while exploring a wooded stream habitat in east Ithaca, the graduate teaching assistant in the class noticed a thick mucusy blob on an alder tree (in the birch family). Alders are fascinating for several reasons, there are a few local species (including introduced European Alder), they have a mutualistic relationship with nitrogen-fixing bacteria (Frankia, an independent origin of a similar relationship between legumes and rhizobial bacteria, the latter of which fixes atmospheric nitrogen in exchange for plant-fixed carbon). Alders are also monecious, meaning that they have separate male and female reproductive parts (in Alders, called catkins) as seen below. Out of fear that the mucus was actually mucus, we initially left it alone. When I can back two days later, I saw two other loogies, so I decided to dig in.  I was rewarded with a juvenile frog hopper (probably Aphrophora alni, the European alder spittle bug).  These spittle bugs feel on plant xylem, perhaps the most nutrient-poor plant substance. Conventional entomological wisdom is that xylem-eating insects need to process so much xylem that they excrete a massive amount of frass (insect poop).  Perhaps they made an evolutionary jump from simply having extra frass to living in a frothy protective bubble.

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Insects trapped the in the mucus of an alder spittlebug next to the male catkins
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Juvenile frog hopper revealed from under its frothy frass

In any case, finding the mucus caused me to notice white waxy clusters on the Alder stems. And looking a bit further revealed the Woolly Alder Aphid, Prociphilus tessallatus

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White waxy clusters of the woolly alder aphid… note the ant on the underside, collecting sugar-rich aphid excrement, likely a mutualistic relationship between ants and aphids
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dense cluster of the woolly alder aphid
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ants patrolling
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Yet, predators find a way, like this spider
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A woolly alder aphid fleas after disturbance

I decided to investigate other alder trees along the edge of the stream and, much more surprising, I noticed a butterfly circling around the aphid colonies. When it tried to land, ants chased it away!  Looking deeper I found the following: Feniseca tarquinius, the harvester, in the family Lycaenidae, and the only North American carnivorous butterfly (okay, there might be a second, see below)

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Feniseca tarquinius, the harvester butterfly
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A harvester butterfly laying eggs in the aphid colony. The eggs will likely be protected from the ants tucked in with the aphids. Then, the caterpillar will hatch and eat the aphids!
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…and grow into this large furry caterpillar (in the center of the image)
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A mature caterpillar just before making its chrysalis
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And the chrysalis, perhaps mimicking bird poop?

Carnivory is very rare among the Lepidoptera… certainly much less than 1% of all butterflies and moths, although it has evolved several times. Of course, the lion’s share of caterpillars eat leaves, and the shift to meat requires various evolutionary changes. On Hawaii, there is even a sit-and-wait predatory moth larvae. On continental North America, the only other potentially carnivorous caterpillar is the cherry gall azure, Celastrina serotina, a newly described species and another member of the Lycaenidae. I found this species a few years ago… it feeds on the galls on cherry trees created by eriophyid mites! What makes its status as a carnivore unclear is that although it eats the “gall” it is unclear to what extent it needs/eats the mite inside

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Caterpillar of the the cherry gall azure feeding away!  The little black spot is its head, poking inside the cherry gall

Fall is also a great time for slug caterpillars. Happy hunting!

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