1. Heat is an important factor in stimulating bed bugs to obtain food. Light and atmospheric humidity do not influence the reactions to heat to any great extent, but the state of nutrition and moulting do interfere with them.
2. The bug detects heat very slowly. At a room temperature of 23° C., from a distance of 4 cm., about 1½ min. were required before a bug reacted to the heat of the hand. At a lower temperature a longer period was required.
3. At ordinary room temperature a differential temperature of about 2° C. was necessary to cause a reaction to heat.
4. Bed bugs, although attracted to heat, will be repelled when the temperature is too high. Bugs were repelled by objects at 43° C. at a distance of about 3 cm.
5. Bed bugs have a sense of smell, but only react when very close to the odoriferous substance.
6. The odours of blood, muscle, subcutaneous tissue and clean, washed skin seemed to have no influence upon the bug; the odour of bile repels them; while liver at first attracted and then repelled them.
7. The odour of perspiration, depending upon its state of decomposition, sometimes repels and at others attracts bed bugs. Of the substances tested the odours of sebum and cerumen had the greatest attracting power.
8. The bed bug apparently discriminates between foods by taste.
9. Negative reactions to water counterbalance positive reactions to heat and odour.
10. The tendency to be in contact with an object, rather than the negative reaction to light, underlies the gregarious habit of the bed bugs as well as their search for places of retreat.
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