Metabolic Rates and Pit-Construction Costs of Two Antlion Species

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Abstract
Resting metabolism and the metabolic cost of pit construction of larval antlions (Myrmeleon carolinus and M. crudelis) were examined. Second and 3rd instar M. carolinus have a lower resting metabolism than similar instars of M. crudelis, while metabolism was similar between 1st instars. Differences between species increased with increasing temperatures. These differences correlate with environmental temperatures of the habitats of each species: M. carlinus is found in hot, open areas, whereas M. crudelis is found in cooler, shaded areas. Antlions are shown to have generally lower metabolic rates than spiders, which in turn have been shown previously to have abnormally low metabolic rates compared to other poikilotherms. The possible significance of these relationships is discussed. Metabolic expenditure during pit constructions was about 10 .times. resting metabolic rates for 2nd and 3rd instar larvae, although this ratio decreased with increasing temperature. Differences in construction metabolism between species were qualitatively similar to resting metabolism: higher for M. crudelis than for M. carolinus. Total metabolic cost of pit construction (the rate of O2 uptake multiplied by the time required to construct a pit) increased with increasing pit diameter. Total cost also decreased with increasing temperature for M. crudelis and for 3rd instar M. carolinus. The energetic consequences of dusk pit-construction are discussed in the light of these relationships between pit cost and temperature.