Monday, July 28, 2008
Bambi is cute fly bait
Cute, isn't it?
Well, the codger's reaction is less adoration than amusement tinged with cynicism.
Here the log-perching Bambi is displaying the heart-warming curiosity of juvenile deer, a fetching trait that renders it highly attractive as fly bait. In fact, a number of mammals are known to be more vulnerable to parasitic fly infestation as juveniles than as adults.
Entomologist John R. Anderson wrote a fascinating paper about the infestation tactics of nose bot flies that parasitize black-tailed deer. (Unfortunately, I can no longer find the paper among 3000 uncatalogued reprints in the garage, so I am jogging my memory and give you the reference below).
You see deer and cattle share a very long history of relations with various species of bot flies that detect their hosts by very general (e.g. CO2 and urine) and very specific chemical signatures, such as volatile compounds from scent glands.
Out here in the west, two species of nose bot flies infest our black-tailed deer. How they zero in on their hosts isn't well known, but Anderson spent a lot of time watching parasitic flies dupe deer.
One species (Cephenemyia apicata), he found, takes advantage of the deer's curiosity.
The gravid fly chooses a bush in plain view of Bambi, and then buzzes about in a come-hither-come-yon dance. Bambi approaches to inspect this curious thing, and is rewarded with a tiny fly larva squirted onto it's moist muzzle. If the deer doesn't lick and swallow it, the larva wriggles into the nostrils.
Cephenemyia jellisoni, the other species, is a stealth hunter. It approaches the deer out-of-sight and from behind, and slowly moves forward beneath the soft underbelly. Then it quietly hovers into position under the animal's throat and muzzle, taking care to remain undetected by tracking the animal's head movements. When the time is right it dashes into position and squirts its larva ('larvaposits') on the moist lips or muzzle. Numerous females may attack a single deer.
The larvae settle in the pharyngeal pouches at the back of the throat, where they feed on tissue secretions and grow into beautiful bots. (I'm kidding of course.)
I still recall my revulsion the first time I saw nasal bots in the throat of a necropsied deer. We were having a wonderful time being young biologists, measuring testes, preserving uteri, while eating curried venison and drinking beer.
When we started to pull mandibles for aging, there they were at the back of the throat: a writhing mass of inch-long white maggots. We gagged and came close to tossing our cookies, but we were tough.
So I don't turn up my nose to insects. They are here to stay, and when nature pits Bambi against flies there's just not much of a contest.
Anderson JR. 1975. The behavior of nose bot flies (Cephenemyia apicata and C. jellisoni) when attacking black-tailed deer (Odocoileus hemionus columbianus) and the resulting reactions of the deer. Can J Zool., 53(7):977-92.
Anderson, JR. and & W Olkowski. 1968. Carbon Dioxide as an Attractant for Host-seeking Cephenemyia Females (Diptera: Oestridae). Nature, 220:190-191
Cogley, TP. 1987. Effects of Cephenemyia spp. (Diptera: Oestridae) on the nasopharynx of black-tailed deer (Odocoileus hemionus columbianus). Journal of Wildlife Diseases, 23(4):596-605
Olroyd, H. 1964. The natural history of flies. Weidenfeld and Nicholson, London
Tømmerås, BÅ., A. Wibe, AC. Nilssen, and JR Anderson. 1993. The olfactory response of the reindeer nose bot fly, Cephenemyia trompe (Oestridae), to components from interdigital pheromone gland and urine from the host reindeer, Rangifer tarandus. Chemoecology 4(2):115-119