Nature Notes in Brief

April 1994

By Terry Morse


When is a mosquito not a mosquito?


Over the last few weeks you may have noticed many large, long-legged, brown “mosquitoes” flying or perched on walls and windows. Examine them closely and you will see that, in place of hind wings, they have club-tipped appendages called “halteres,” which function as stabilizers in flight. The presence of halteres reveals that these are true flies, members of the order Diptera. Mosquitoes are also flies and have halteres, but these are not mosquitoes.


The mosquito look-alikes are crane flies (family Tipulidae). Unlike female mosquitoes, they don't bite. The larvae live in water or moist soil, feeding on decaying plant material. The adults of most species exist only to mate and do not eat, though a few sip nectar. Some species have colorful wing-markings. One species that may be seen in Oregon, the giant crane fly, Holorusia grandis, can be more than an inch long with a nearly 3" wingspan.


Jaws


Garter Snakes (Thamnophis species) are among the commonest and most readily seen snakes along the Oregon Coast. Four species occur in the Pacific Northwest, two of which are likely to be seen in Lincoln County: the Northwestern garter snake, Thamnophis ordinoides, and the common garter snake, Thamnophis sirtalis. Both are dark brown or black snakes, typically with a green or yellow stripe down the back and possibly on the sides as well. The common garter snake has varying degrees of red markings, from spots on the side to bright red on the top and sides of the head (the red-spotted garter snake, Thamnophis sirtalis concinnus). The first red-spotted garter snake I ever saw, I thought had been run over by a car and was bleeding from the head, but it was just normal coloration.


The typical food for both species is cold-blooded animals, such as earthworms, slugs, frogs, and salamanders. The red-spotted garter snake is unusual in that it is able to eat the highly poisonous rough-skinned newt (Taricha granulosa), apparently without ill-effects. Related species, and subspecies of common garters outside of the newt’s range, lack this immunity and may die simply from holding one of the newts in its mouth. Neurobiologist Don Campbell has speculated that the bright red markings of the red-spotted garter could be warning coloration: perhaps the snakes are able to store the toxin from the newts for their own defense. This could be tested by feeding a red-spotted garter snake to a snake predator, as long as you don’t mind possibly losing the predator to the toxin, if it is there.


Garter snakes will occasionally eat warm-blooded prey, such as small mammals and birds. I discovered this rather graphically on the afternoon of April 28th . Walking along the Hatfield Marine Science Center estuary trail around 2 pm, I heard pitiful squealing from the grass opposite the trail’s north shelter. Stalking closer, I saw a red-spotted garter snake resting on top of the grass. As I approached, the snake pulled back into the grass a little, and I saw that it was in the process of swallowing a vole (meadow mouse) tail first. The vole was still alive and in great distress, its eyes clamped tightly shut. There was nothing I could do to save the vole short of killing the snake, and I don’t think it would have been ethical to interfere even if I could have. The incident was a pointed reminder that life can be very harsh. The vole was still crying out five minutes later, when I left. By 2:30, when I passed that point again, it was all over except for the digesting. I still shudder thinking about it, one of the costs of empathy.


Garter snakes can often be seen in summer, warming themselves on the asphalt of the nature trail. Watch well ahead along the trail and you may see them before they can slither off into the grass. Freeze, and you may be able to watch them for several minutes before they flee.


© Terry Morse


Revised: July 7, 2004