Backyard Biology

Nature stories from my backyard and beyond

Nature Stories

Moths and Wasps

Tuesday, August 13, 2013

If you notice a small hummingbird (small by hummingbird standards) feeding at a flower that hummingbirds do not usually frequent , take a closer look. You may be looking at a Hummingbird Clearwing Moth. These moths are distinctive for a couple of reasons. First, unlike most moths, they fly during the day. Second, also unmothlike, they have the ability to hover in mid-air. This is accomplished by the incredible speed at which their wings beat. You can often see these moths hovering in front of a flower, using their long tongue to sip its nectar. This hovering ability and the moths large size cause many people to mistake them for hummingbirds.
The hummingbird clearwing holds a special place in my heart. Not content to skulk around in the dark like its brethren, it seems to revel in the sunlight as it hovers at the flowers of our garden, sipping their nectar. Is it just my imagination, or does the hummingbird clearwing truly enjoy life? If I were an insect, I could be content to be a hummingbird clearwing moth.
This fall, I found my first hummingbird clearwing caterpillar. caterpillarIt is a smooth green affair with white stripes running lengthwise along its back. Extending from the back end is a reddish spike, pointing upwards. Attached to the caterpillar’s back were about two dozen structures that looked like grains of rice.

Braconid wasps are about an eight of an inch long. You would never notice these insignificant wasps as they feed on the nectar of flowers, especially if you were enthralled watching a hummingbird clearwing feeding at the same clump of flowers. Noticed or not, the braconids must still eat. And they must also reproduce. After mating, the female brachonid wasp will locate a suitable spot to lay her eggs. In one particular species, that spot is the body of a hummingbird clearwing caterpillar.
This egg-laying must be done with care. The eggs are laid in the caterpillar in such a way that when the eggs hatch, the larval wasps feed only on the body fluids of the caterpillar and not injure any of the caterpillar’s vital organs. It would do no good for these parasitic wasp larvae to kill the caterpillar while the wasps still need a food supply. The caterpillar must eat for the wasps as well as itself.
When the wasp larvae have reached full size, each one will eat its way out of the caterpillar and spin a cocoon around itself. In this cocoon, it will transform itself from the larval to the adult wasp, and the life cycle will be repeated.
The rice grains on the back of my caterpillar were the cocoons of the brachonid wasps. There was not much left of the caterpillar. It had a couple of dozen holes in its body where the wasp larvae had emerged. However, the larvae were so skillful at avoiding all vital organs that the caterpillar was still alive and continued to feed for the next few days!

Scenes like this remind me how desperate is life’s struggle in my back yard. Perhaps it is better to be the insignificant wasp than the sun-loving moth.

As I was carrying the caterpillar home for a closer look, I noticed two wasps climbing over the cocoons. Are the cocoons hatching? Excited that I might be able to see what the adult braconids might look like, I placed the caterpillar under my microscope. What is this? The wasps are stinging the braconid cocoons. I have found a hyperparasite, an insect that parasitizes a parasite. These wasps are laying their eggs in the cocoons of the braconid wasp parasite.

This story is not over yet. Now I must wait to see what emerges from the cocoons. Do these last wasps have parasites of their own?

While all animals have their own special set of parasites, only the human species can take a perverse pleasure in enjoying the parasites of others.