Figure 1
Photographs of hornets taken with infrared cameras capable of temperature discrimination. The image in (a) was taken in summer 1998 using a Thermacom Model 290 PM camera and processed by commercial Thermonitor 95 software, both from Inframetrics USA. The images in (b)–(d) were recorded in October–November 2002 using a FLIR ThermaCam SC500 (
) and a PC card interface Agema THV550, and were analyzed by software application ThermaCam Researcher version 2001. (a) Hornet anesthetized in its natural nest at night by ether vapor, lying on comb before recovery. (b) Similarly anesthetized hornets, at daytime in the laboratory, lying on comb during recovery stage. In (a), the color coded temperature and exhibited spot measurements of body temperature reveal that the outer shell of the hornet is as much as
cooler than the comb. In (b) one can discern six hornets in the recovery stage from ether vapor anesthesia. A hornet slightly to the right of center and two others at the lower right side are cooler than the comb. All three exhibit coldest temperatures in small isolated regions or spots. In the case of the hornet near the center, one such cold spot is located at the tip of the abdomen and an even colder spot is located at or near the compound eyes. The latter cold spot is
cooler than the comb. Above this hornet, another one can be discerned whose wings are cool though its body is warm, compared to the comb. More to the left are two more hornets with warm bodies, and even warmer heads: The head temperatures are up to
warmer than the nearby comb, and
warmer than the cold eyes of the central hornet. (c), (d) Routine activity near the entrance to a natural hornet nest which the wasps built and maintained during an entire active season (May through October 2002) in a plywood box positioned on a laboratory window sill. The entrance can be discerned as a circular hole of diameter
in the box wall at the bottom, where the apparent temperature is somewhat higher than the exterior surface of the wall. In (c) a hornet is seen walking on the exterior of the wall just before it enters the nest, after having flown in several seconds earlier from an outing. In (d) a hornet is seen who has just exited from the nest, and is about to take off on a foraging flight. In this case, both the thorax and the abdomen are apparently somewhat warmer than the surroundings, though not warmer than the nest interior, but the wings are cooler, by about
, than the plywood outer nest wall.
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