I spotted this impressive sight early this summer. A dozen or so acrobat ants gripped and suspended a huge caterpillar upside down from a tree branch above me, as other workers started to pick it apart. As arboreal ants, acrobat ants have some of the most impressive gripping ability I have encountered. I judge this by the time I have spent aspirating ants from trees for various projects for the lab–in particular the day I helped the post-doc collect several groups of 50 of these guys. These guys can really hold on. By the end of an hour I was light-headed from the aspiration attempts, and reduced to using the tube to try to pry the ants loose.
In fact, as Myrmecos author Alex Wild brought up a while back, a number of plants have adapted to take advantage of arboreal predators by providing wooly footholds to help them hold on.
Here’s an immature form of the swallowtails we saw in the last post. Late instar swallowtail caterpillars like the one above have aposematic coloring, warning of the toxic chemicals they have gradually sequestered from the plants they eat. Swallowtail caterpillars also have another unique defense mechanism–an organ called the osmeterium, located in the head. When threatened, caterpillars evert the osmeterium, which resembles two brightly colored fleshy ‘horns’ on the caterpillar’s head. The osmeterium emits foul-smelling terpenes which, along with the startling appearance and the caterpillar’s thrashing movements, helps to ward off predators.
Just got back from the ESA conference in San Diego! It was fun.
Here’s some pictures I took last spring at the gorgeous flower field outside La Bahia (Goliad, Texas). Two common varieties of Texas swallowtail butterflies, family Papilionidae, feeding in the flowers. Swallowtails take their name from the long ‘tails’ common on the wings of butterfly species in this family. Butterflies feed through siphoning mouthparts in the form of a long, coiled tube, called a proboscis. As lepidopterans metamorphose from caterpillars to butterflies their mouthparts change drastically from leaf-chewing mandibles to a nectar-sipping tube. This change is mirrored in their digestive tracts, which in caterpillars take the form of a fairly simple tube, and in butterflies becomes much more complex.
Most people are comfortable differentiating butterflies and moths. However, as with most biological groupings, especially those based more on appearance and habits than taxonomy, exceptions and ambiguities run rampant. One particular example, is that of the ‘skipper.’ Perhaps this common name is, in fact, commonly used by other laypeople, but I had never heard of it when I entered entomology. If I had seen a skipper in the field, I would probably have assumed it was a moth still out in the daylight, or a somewhat odd and drab little butterfly.
In fact, skippers are a subgroup of butterflies, comprising the family Hesperiidae. They resemble a cross between a moth and a butterfly, but can be easily recognized by several features. They have large, wideset eyes on a broad head, one of the characteristics that lends them a moth-like appearance. Their antennae are also widely set, not meeting at the base, and have hooked clubs at the ends. Their stocky bodies tend to be fairly fuzzy or fluffy looking and they have drab to moderately bright coloration.
Skippers are active in the day time, and take their common name from their quick, short flying style. Many species look quite similar to each other and can be difficult to distinguish. These butterflies are both extremely common and widespread. I took the photo above of a skipper in Argentina, while the mating pair below I spotted in the Welder Wildlife Refuge in Texas.
The frantic fluttering of this skipper caught my eye at one of the Argentinian field sites. The mantis that had snatched the little butterfly had only got hold of one wing, and couldn’t quite seem to manage to get her lunch under control. After a valiant struggle, and some munching on the wing, she eventually lost her hold, leaving the mantis hungry, and the skipper crippled on the ground below. Being a bug is not much fun.
Quite a number of insects have independently evolved raptorial forelegs for capturing their prey, but mantids (order Mantodea) are by far the most well known for this feature. Raptorial means ‘grasping’ or ‘adapted for seizing prey’ — think of the talons of birds of prey (raptors) or those of the cunning velociraptors from Jurassic Park. The opposable spines on the mantid’s front tibia and femur fulfill a similar purpose, and their long reach and speed make them dangerous predators in the insect world. Mantises have even been known to lurk on hummingbird feeders and pick off the unwary bird.