Friday, July 29, 2011

Heads or Tails?

In spite of its psychedelic complexion and robust build this Promethea Moth (Callosamia promethea) proved difficult to spot amongst the foliage.

I've inserted my pinky finger in the picture to give an idea of the size of this insect, but it's scared and has hunched itself up somewhat, making it about ten centimeters shorter than its normal length ... about the same as my finger.

Chowing down on some yummy White Ash leaves ...

Note in the images above that the head has no bold colors or patterns, and the insect pulls it under its body when it feels threatened. Now consider these views with an emphasis on the posterior end. The terminal pro-legs or pseudopods are large, bear a black circular mark that suggests an eye, and are left in plain sight. (Pseudopod → "false foot" ... insects have only six legs, they are visible just behind the head in this photo).

Eyes can betray an animal's position to a potential predator, and many organisms sport bars or camouflage patterns to disguise them. By the same token, note how many butterflies, fish, etc., often sport fake eyespots on hindwings or tail fins. Are the eyespots targets to draw a strike to a non-vital area, or to make an otherwise innocuous species look threatening to a hungry hunter? Here's some thought-provoking reading: Why eyespots?.

And where, you say, is the "moth" in these photos? That lies in the future ... first, this caterpillar will overwinter as a pupa, and with luck this story will continue next year ...

The Orange-Humped Mapleworm Moth (Symmerista leucitys) adopts similar "false head" plan of action if it feels endangered. Although the head is a bold shade of orange the back end also bears prominently colored red and orange markings, and it holds its posterior the air with the last pair of prolegs splayed open. Everything about the caterpillar's posture suggests a head with antennae – at the non-vital backside of the insect.

The two appendages at the tail end of this Furcula Moth (not sure what species) larva also look very much like antennae.

The slow moving, soft-bodied larva of the larva of the White Admiral (Limenitis arthemis) makes a yummy morsel for a hungry bird. This caterpillar increases its chances of survival by not only being colored like ...

... but adopting the posture of, an inedible and not-so-tasty bird dropping.

Some species make themselves distasteful or toxic to minimise predation. The larva of the Monarch (Danaus plexippus) ingests the toxins found in its food plant, the Common Milkweed. The caterpillar's bold yellow, white and black stripes advertise its unpalatability.

Presumably the Milkweed Tussock Moth (Euchaetes egle) also toxic for the same reason, and hair or bristles can also be a deterrent to being captured and swallowed. But what's with the grouping? Are they mimicking a larger animal? Or is it a matter of safety in numbers like a flock of birds or a school of fish ... any single individual is less likely to be targeted?