Monday, October 12, 2009

Intoxicating Insects

Back in August, Bug Girl posted a call for participants to trap hornets and yellowjackets. The USGS is trying to develop survey techniques for these insects that could be repeated on a large scale. For this project, volunteers were asked to fill a clear plastic bottle partway with beer or fruit juice and leave it hanging for three weeks in an area that hornets might visit. (You can read the details at Bug Girl's Blog linked above.) I hung my beer trap over one of the gardens and then mailed the specimens to the USGS. The beer I used was Lord Chesterfield Ale; I wanted something that would be cheap but drinkable.

Sadly, the brew only attracted a single yellowjacket and a sweat bee. The yellowjacket was a German Yellowjacket (Vespula germanica), the insect pictured below. Kaufman's insect guide notes that this introduced species has become a pest due to its tendency to nest in walls. It is also an unwelcome guest at picnics and barbecues. When not scavenging the food and trash of humans, these yellowjackets prey on insects, including some pest species. Live yellowjackets should be treated with caution since they can be aggressive and have a painful sting; this one was pretty harmless.

Although this trap was short on Hymenopterans, it had captured plenty of other insects. Most were tiny flies or gnats, too small for me to identify and even difficult to separate from each other without damaging the specimens. There were also several larger flies, one of which was quite big. The lump in the top right of the photo below is a mass of tiny flies held together by the moisture. I think the fly on the lower right is a house fly (Musca domestica) and the one on the lower left is a Tachinid (family Tachinidae). Tachinids parasitize other insects by laying eggs on them. When the eggs hatch, the larvae feed on the host insect, killing it in the process.

In that photo you can also see a moth, which is shown in more detail below. Since the wings have been curled by the moisture and most of its markings dissolved, it would be impossible for me to identify the species.

There was also a second larger moth, pictured below. The wings on this specimen show more of their shape, but unfortunately they too have lost their markings. One detail I found interesting is that the body on this moth seems significantly longer than its wings. Most of the moths I have been seeing show the opposite.

The beer trap also caught a cranefly. This is not a Giant Cranefly like the ones I posted last month, but I am not sure of the species.

This was a fun exercise, and I am glad that I participated. Perhaps if I had hung my trap a week or two sooner, it would have collected a few more of the target species. I noticed more bees and wasps around that garden in the weeks prior to hanging the trap than in the three weeks after. In any case, I would encourage readers to participate if the opportunity comes up again.