Brown Legged Grass Carrier

Isodontia (Murrayella) auripes (Fernald)

This sphecine wasp preys primarily on crickets (Gryllidae), but occasionally it also stores one or two shield-backed katydids (Tettigoniidae) in the brood cell. I was able to make observations on the nesting behavior and development in two nests in 12.7-mm traps, numbers 127 and 107. Trap 127 and three others of the same diameter (122, 125, 126) were set out 10 April beneath part of a wooden frame (Figure 3) supporting a Strophanthus bush in a cultivated field. I observed carpenter bees, Xylocopa virginica krombeini Hurd, emerging from borings in this frame, and I set out only large traps in an attempt to induce nesting by these bees. The other trap was set out 9 April beneath a dead branch of a live scrub hickory (Figure 2) at the edge of a fire lane through the slash pine-turkey oak association in a wooded area quite open to the sun. The traps at both stations were about 1.5 m above the ground.

Nesting Behavior

I checked both of these stations several times a day. The first evidence of auripes at either site was at 1145 on 12 April when I noted a female entering and leaving trap 125, flying around for a few seconds, then entering trap 126, and finally leaving the area entirely. Nesting had not begun in any of the traps at this station. At dusk that evening, 1845, this or another female of auripes was resting inside trap 122. At 0815 on 14 April the sky was overcast and this female was still in 122. On that same date by 1900 she was resting in 127 where she had brought in some pieces of grass stem and blades. She was still in trap 127 at 0800 on 15 April. At 0925 the wasp was still inside the brood cell and had begun to build up the closing plug. At the already sealed inner end she had earlier constructed a plug of compacted, coiled grass stems; it was 10 mm thick in the middle and 13 mm at the edges. Two hours later I rechecked this trap and found the wasp facing inward near the opening and compacting the materials forming a closing plug by pressing with her head. My examination of her nest disturbed the wasp, so that she turned around and flew out. The brood cell, 80 mm long, contained a paralyzed false-jumping bush cricket (Orocharis luteolira T. J. Walker) lying on its belly, head inward next to the plug at the inner end; it bore a pale, yellowish-green wasp egg. The temporary closing plug was 35 mm long and was composed of loosely packed stems and fibers in the inner 25 mm and densely compacted fibers in the outer 10 mm.

My next visit to this station was an hour later, at 1240 on 15 April. During that period auripes brought a second paralyzed specimen into the brood cell, a large tettigoniid nymph (Atlanticus gibbosus Scudder), which she placed on its belly, head inward next to the bush cricket stored earlier. I removed the plain strip of wood to permit photography through the plastic and could see the abdomen of this tettigoniid pulsating rhythmically. I was unable to see whether it bore a wasp egg. Shortly after 1300 the auripes returned with another paralyzed bush cricket, which she left venter down in the outer 30 mm of the trap while she excavated a passage through the closing plug (Figure 6). She entered the brood chamber, pushed the earlier prey closer together, turned around and went out through the closing plug head first. Turning around again, she grasped the head end of the cricket with her mandibles (Figure 7), and carried it venter down through the passage in the closing plug. Once inside the brood chamber, she dropped the cricket, turned around on her back, grasped the head end of the cricket with her mandibles (Figure 8), and dragged it up above the tettigoniid nymph. Then, continuing to lie on her back, she turned the cricket on its side, curled her abdomen upward (Figure 9) and deposited an egg between the fore and mid coxae. Next, she pushed this cricket, now venter up, to the inner end of the brood chamber on top of the first two prey (Figure 11). About 1315 she left the brood chamber, pulled out some fibers from the outer end of the plug, and proceeded to work on the plug to form a tighter closure (Figure 10). At 1327 she flew away, leaving some loose fibers in the outer 40 mm of trap 127. Exposing the nest to light and using the electronic flash for photography did not appear to affect the behavior of the wasp in 127 whatsoever. This auripes had not returned by 1335.

Upon my next inspection of nest 127 at 1440 on 15 April, I discovered that the wasp had brought in a fourth cricket. She had also dragged the third cricket down from on top of the tettigoniid nymph and placed it on its back behind that prey. She flew back to the nesting site at this time, apparently not carrying any prey, and flew off in a few seconds without entering the nest. The wasp was not in the nest at 1545, but at 1845 she was resting there for the night, facing outward in the outer end of the boring, with her abdomen against the closing plug. She left the nest before 0830 on the 16th, and sometime during the morning she brought a fifth cricket into the nest (Figure 12). There was no further nesting activity at 1240 or 1330, so I brought the nest into the laboratory for further photography and weighing of the prey. This wasp never began a second nest at this station, even though empty traps were available.

Another female auripes began a nest in trap 107, half a kilometer distant from trap 127, during the 3-day period 12–14 April. When I checked Station 14 at 0900 on the 15th, I found that trap 107 contained a plug of compacted Spanish moss strands 5 mm thick at the inner end, an empty brood cell 65 mm long, and a temporary closure of tightly packed Spanish moss about 15 mm thick. Trap 108, adjacent to 107, contained a few short strands of Spanish moss near the inner end; there was no subsequent nesting activity in the former trap, so it is likely that the wasp nesting in 107 may have placed the moss in 108 before or during preliminary nesting activities in 107. While I was examining the traps, a large insect, possibly the Isodontia, buzzed around my head and flew off before I could identify it.

The female auripes was in the outer end of nest 107 at 1350 on 15 April. She flew off when I shone a flashlight into the trap. At this time the nest contained three paralyzed false-jumping bush crickets lying on their backs, head inward, each bearing a pale yellowish-green wasp egg affixed to the venter of the thorax. I returned to 107 at 1415 and for the next 15 minutes I watched the wasp bringing in plant materials to add to the temporary closure. At 1421 she carried in a piece of grass stem about 5 cm long. It took her 2 minutes to work this into the plug, after which she flew around the immediate vicinity, alighting here and there on dead plants, and trying unsuccessfully to pull off some of the curled, dried leaves. In a few minutes she brought in a piece of Spanish moss about 8 cm long, worked it into the plug for 3 minutes, and then flew out of sight. When I returned at 1551, she flew out of the trap, and I discovered that she had brought in a fourth cricket during the interim and had laid an egg on it (Figure 13). At 1850 that evening she was resting at the outer end of the trap with the tip of her abdomen against the temporary closure; there were still only four bush crickets in the brood cell.

The wasp had already left 107 when I made my first check of that nest at 0820 on 16 April; the nest appeared the same as it had the previous evening. Five minutes later the auripes alighted for an instant at the nest entrance and then flew off; she carried neither prey nor vegetation. The wasp flew out of 107 when I returned half an hour later; again, there had been no nesting activity in the interim. The wasp did not return during the next half an hour. However, by 1045 there had been additional nesting activity (Figure 14). One of the earlier prey specimens had been piled on top of the first one at the inner end, another prey had been brought in, and the wasp had left a pile of loose vegetation (Figure 15) at the trap entrance. I checked 107 several times during the afternoon, before removing the nest at 1600, and noted no additional nesting activity. However, subsequent examination in the laboratory disclosed that a sixth prey had been stored during the 16th.

Nest Architecture

Figure 14 shows the architecture of a nearly completed auripes nest with a narrow plug of vegetable fibers at the inner end, a brood cell, and a thicker closure of vegetable fibers thoroughly compacted in the outer portion of the plug. It is quite likely that neither of these nests had been completed when I picked them up during the afternoon of 16 April. Normally, when auripes makes a final closure, she brings in grass stems and blades which she places along the axis of the boring at the outer end, protruding from the entrance (Krombein, 1967, p. 247).

The plug at the inner end of the boring in 127 was about 12.5 mm thick and consisted of tightly coiled and compressed grass stems and blades (Figure 16); whereas, in 107 the plug was 5 mm thick and made from coiled, compacted strands of Spanish moss (Figure 18). The brood cells were 57 mm long in 127 and 64 mm in 107. The closing plug of 127 was 41 mm thick and was composed of pieces of dried vegetable fiber and grass blades, loosely packed on the inner (left) half and firmly compacted on the outer half (Figure 17). In nest 107 the closing plug was of the same thickness: the inner, loosely packed half was made from strands of Spanish moss, the outer, closely compacted half from small pieces of plant stems having rather long woolly hairs (Figure 19).

Prey

These two individuals of auripes preyed principally on the false-jumping bush cricket Orocharis luteolira T. J. Walker (Figure 20) and, less frequently, on the shield-backed katydid Atlanticus gibbosus Scudder (Figure 21). The wasp in 127 used only adult Orocharis and a nymph of Atlanticus; whereas, the wasp in 107 used both nymphal and adult Orocharis and nymphal Atlanticus. Both sexes of Orocharis were preyed upon, but only nymphal males of Atlanticus. Dr. T. J. Walker, who was able to identify both prey species from fragments remaining in the nests and from photographs, commented that in his experience Orocharis never descends to the ground whereas Atlanticus nymphs seldom ascend from the ground, especially during the day when auripes would be hunting for prey. This suggests that auripes exploits several ecological niches while hunting for prey.

All specimens of prey were thoroughly and permanently paralyzed, and were capable of only weak reflex actions of their antennae, mouthparts, and legs. Feces were voided for a day or two after the prey were stored. In nest 127 each of the crickets lacked a hind leg; these may have been amputated by the wasp.

Table 2 presents information on the prey stored in these nests: their sex, identity, length, and their fresh weight after voiding feces. The specimens are listed in the order in which the wasp arranged them in the nest, 127–1 being the prey at the inner end on the bottom and 127–5 the prey nearest the outer end. It should be remembered, however, that both wasps did some shifting around of specimens subsequent to the prey being brought into the nests. Consequently, it must not be assumed that the order in which I list them is necessarily the order in which they were caught. Prey specimens 127–1, 3, and 5 each bore a wasp egg, as did the first five of six prey in 107; these eggs added an infinitesimal amount to the fresh weight of the prey. The mass fresh weight in nest 127 was 930 mg or 310 mg for each wasp egg; similar figures for nest 107 were 840 mg and 168 mg.

Prey

number Prey identity Length

in mm Fresh

weight

in mg

127-1 Orocharis, adult 17 190

127-2 Atlanticus, nymphal 16 290

127-3 Orocharis, adult 14 120

127-4 Orocharis, adult 17 190

127-5 Orocharis, adult 15 140

107-1 Orocharis, adult 15 120

107-2 Orocharis, nymphal 12 95

107-3 Orocharis, adult 17 185

107-4 Orocharis, nymphal 11 110

107-5 Atlanticus, nymphal 13 115

107-6 Atlanticus, nymphal 14 215

I captured a pair of adult Orocharis luteolira which had spent the night in two empty traps. The female was 18 mm long, the male 17 mm, and the fresh weights were 239 mg () and 166 () before voiding feces. Each was held for 24 hours, then killed and dried thoroughly in an oven. The resultant dry weights were 67 and 49 mg respectively, a weight loss of a little over 70 percent. Applying that reduction factor to the average weights of prey stored per wasp egg, it is calculated that 93 mg dry weight was provided per egg in nest 127 and 50 per egg in nest 107.

Adults of auripes were so uncommon that I was not able to capture and weigh any of them. However, I did obtain a series of six female and male Isodontia (Isodontia) exornata Fernald, a species of comparable size. These specimens were 17–19 mm long and had fresh weights of 80–123 mg. After thorough drying in the oven, the resultant dry weights were 28–48 mg, a reduction of 61–65 percent.

Life History

The sausage-shaped eggs were slightly curved, pale yellowish green, 3.4 mm long and 0.75 mm wide. The anterior end was glued firmly behind the fore coxa and the egg was placed transversely across the sternum so that the posterior end extended beyond the side of the thorax opposite the egg attachment (Figure 22). In nest 127 two of the eggs were attached behind the right fore coxa, one behind the left; in 107 four eggs were attached behind the left fore coxa and only one behind the right.

Larvae hatched from the eggs in 52–54 hours in the five cases where reasonably close information was available on the times of oviposition and hatching. Body segmentation was visible through the chorion for several hours before hatching occurred. The newly hatched larvae began to suck blood at the point of attachment of the egg. Feeding was slow in the younger stages, and the larva required about two days to empty completely the prey on which the egg has been laid. I photographed the development of the youngest larva in nest 107 at periodic intervals over this 2-day period (Figures 23–30). The prey had been so thoroughly gutted by the end of the second day that the head and anterior part of the thorax separated from the rest of the body when I removed the specimen from the nest. After emptying the body contents, each wasp larva continued to feed on the exoskeleton, devouring almost all of it but fragments.

When the older larvae finished feeding on the original specimen of prey, they wriggled to one of the untouched prey, if any, and began to feed on it (Figures 31–32). Thus, the two older larvae in 127 finished their original crickets at 0800 on 20 April; by 1155 one of them commenced to feed with its head inside the abdomen of the tettigoniid nymph, and by 1600 both larvae were feeding through the thorax of the two prey specimens which did not originally bear eggs. The larvae in both nests continued to feed on fragments of the exoskeletons for the next day or two (Figures 33–34). On 22 April at 0800 the three larvae remaining in 107 finished feeding and began to pull strands of Spanish moss into the brood cell (Figure 35); they continued to pull Spanish moss into the cell until at least 1600 (Figure 36). The two larger larvae in 127 continued to feed on prey fragments until 0800 on 23 April. By midmorning one of these larvae had caught the anterior end of its body in the hollowed out thorax of the tettigoniid and was unable to extricate itself; it died several days later. The larvae in 107 consumed all of the prey except for parts of the exoskeleton whose dry weight totaled 55 mg; in 127 the larvae left uneaten 108 mg dry weight.

The three larvae in 107 and one larva in 127 began spinning cocoons between 1900 on 23 April and 0800 on 24 April. The cocoons were constructed among pieces of dried plant materials which the larvae pulled from the inner end of the closing plug and among the fragments of the prey (Figures 38–39). The larvae had not been spinning for too lengthy a period by 0800 because they could still be seen through the white silken cocoon walls at that time (Figure 37). By 1915 on 24 April the walls of the white inner cocoons were so dense that the larvae could not be seen through them. On the following morning at 0800 the inner cocoons were light tan, indicating that the larvae had impregnated them, probably with liquid fecal wastes. No information was obtained on the date of pupation because I did not open the cocoons. A male auripes emerged from nest 107 on 7 June and a female from nest 127 on 8 June. Thus, the life cycle from egg to adult in these nests was about 54–55 days.

There was a high mortality rate in both nests but very little, if any, was due to cannibalism. In nest 127 where there were three eggs, the youngest egg never hatched and one of the mature larvae died after getting stuck in the hollowed-out thorax of a prey. In nest 107, where there were six eggs, one larva died two days after hatching, the youngest larva (the subject of Figures 23–30) died from lack of food, two larvae died in cocoons, and one adult emerged. The fate of the sixth larva in 107 was not ascertained. It just disappeared one day and may have been cannibalized.

Isodontia auripes, the brown-legged grass-carrier, is a species of thread-waisted wasp in the family Sphecidae.

Brown-legged grass-carrier, Isodontia auripes