Leafcutter ant 'hitchhiking'

A minor worker rides on a cut leaf

 When watching a foraging trail of Atta cephalodes leafcutter ants, you will likely notice that occasionally a smaller ant will be 'hitchhiking' on a leaf fragment that a larger ant is carrying.  At first look, these ants appear lazy but they are actually providing a critical service to their colony.

In many habitats, these ants are attacked by flies in the family Phoridae.  Female flies alight on leaves in transport, crawl towards the carrier, and lay eggs on the unwitting ant.  When the eggs hatch, they enter the ants body and consume it from the inside out, eventually killing it.  Hence the reason for the seemingly lackadaisical passengers.  A fly is much less likely to land on a leaf with a rider, and if it does it will quickly be chased off.  The minor workers are defending their sisters from aerial parasitoid attacks.

If you are worried about flying parasitoids, for a small fee I will ride around on your shoulders for a day, defending you from various forms of death from above.

First monarch sighting of 2012

A 2010 monarch lays an egg on milkweed

 While the Journey North webpage indicates that my old friend Danaus plexippus has been in Delaware for some weeks, I saw my first female this past week.  The migratory female that I saw was drab colored and ragged, which suggests to me that it may have traveled quite far this Spring.

  Some of the common milkweed that we planted 2 years ago is just barely starting to poke through the soil, but it's a ready target for ovipositing females.  We may have the only Asclepias in the neighborhood, and a female kept circling back and searching for an open spot to place an egg.  The tip of the milkweed ramet below already had 7 pinhead-sized eggs on it!  Monarchs have high mortality in the early caterpillar stages, and milkweed grows quickly from its underground rhizomes, so there should be plenty of food for everyone when they hatch.

Monarchs are good at finding their Asclepias host plant, even when it is barely poking above the ground.

A native stink bug

Brochymena on Juglans

Camouflage and Warning

You can't see me!  This caterpillar blends in with mosses and lichens on a tree trunk.

The advantage to blending in is obvious; cryptic animals (like the caterpillar above) are less likely to be found by predators.  Selection for crypsis is so strong that many animals alter their behavior to enhance their camouflage.  Other animals, however, sport bold colors as a clear message to would-be enemies: Stay away!

Tetrio Sphinx Moth, Pseudosphinx tetrio

These aposematic patterns are common in caterpillars that are toxic to predators.  The Sphinx moth above is harmless on the outside, but inside it contains chemicals that it has accumulated from its host plants in the Dogbane family (plants with -bane in their names are often poisonous).  The same concept applies to other bad tasting, dangerous, or poisonous creatures like this poison dart frog:

Oophaga pumilo warns that it is poisonous. It accumulates toxins from tiny invertebrates that it eats.

So why don't these toxic animals double-up on defense and use camouflage too?

Without a warning signal, a bird would have to peck a to determine that it tastes bad.  The prey might not be eaten, but still die from its wounds.  Bright colors may also help predators learn quickly and remember their bad experiences with prey.  Predators are also more cautious when pursuing bright colored prey, affording extra opportunities for escape.

There are also costs associated with being camouflaged.  Crypsis only works when an animal stays on the correct backdrop, and usually only when it is staying still.

I'm a leaf.

This frog was so well suited to the fallen leaves that it was only spotted because it moved.  I looked away momentarily, and was unable to find the frog a second time.

Green and Black Poison Dart Frog

Dendrobates auratus with parasitic nematodes in skin