Two surface behaviors were described in the larva of the antlion V. americana. Vella americana were observed flicking in a similar manner to pit builders, but in a way that does not lead to pit construction. A new spyhop behavior also was observed in which a larva exposes its head and thorax above the sand and remains very still for some time. It is hypothesized that these behaviors assist larval V. americana in hunting and orientation. The flicking motion may attract the attention of certain prey species, and the spyhop exposes the larva's stalked stemmata and multi-segmented antennae to increase sensitivity to prey or disturbance.
Sand-dwelling antlions in central Florida are non-invasive, nonendemic organisms that nevertheless thrive in the Florida scrub, a rare xeric ecosystem with a remarkably high rate of endemism (Deyrup 1990). About 85% of pre-Columbian Florida scrub has been lost to development or conversion (Craddock 2008). The sand roads at Archbold Biological Station provide habitats for plant and animal species that ordinarily colonize gaps produced by fire or the allelopathic litter of Ceratiola ericoides Michx. (Ericaceae) (Menges et al. 2008). This human-facilitated environment supports a dense community of sand-dwelling antlions, including several species of pit-building Myrmeleon and surface-walking Brachynemurus (Stange 1980). While the charismatic pit-building species are frequent subjects of behavioral observation, the actively hunting genera are not well known. Sand roads at Archbold Biological Station therefore provide an opportunity to observe and collect larger numbers of antlion larvae than may be found in natural foliage gaps.
Vella americana (Drury) is an acanthaclisine antlion found in the southeastern United States and Mexico, and possibly the largest antlion in the Western Hemisphere (Miller & Stange 1985). Larval V. americana require deep, loose sand in order to conceal their defenseless bodies and enable them to burrow. This author has observed only backwardswriggling movement in this species, with the muscular abdomen producing most of the force, and so it appears that V. americana cannot walk forward like the Brachynemurus that share its habitat. The habits and behaviors of V. americana have received little attention or study.
Live collection and in situ observation were conducted at Archbold Biological Station between Mar and Jul 2016. Thirteen V. americana were raised in captivity for 3 mo and at least 20 others were held captive for a few days at a time. As this species does not construct pit traps, individuals were located by following their burrow trails. In captivity, hunting V. americana lie in wait for prey to walk over their jaws, and often burrow towards and around mobile prey to better facilitate striking. After seizing prey, larvae quickly disappear beneath the surface. Larvae readily accepted any prey they could catch and submerge, including beetles, ants (Pogonomyrmex badius Latreille [Hymenoptera: Formicidae], Florida harvester ant), moths, myriapods, isopods, and arachnids.
Although larval V. americana display the flicking motion that is characteristic of pit-building Myrmeleon, they do not use this tactic to excavate pits (Fig. 1). Flicking serves several purposes for pit-building antlions, including excavating and maintaining traps, discarding debris, and directly striking prey to encourage pit wall collapse (Heinrich & Heinrich 1984). The occasional flicking and associated substrate tossing of V. americana does not serve to produce the excavation depth seen in Myrmeleon, as the latter burrows in a tight spiral and repeatedly tosses substrate from the same area. This author has observed only flicking in V. americana when prey insects are active on the sand surface posterior to the larvae. Because there are no loose pit walls, striking prey with sand cannot have the dislodging effect that Myrmeleon rely upon to bring prey within striking distance. It is hypothesized that flicking by V. americana serves to attract the attention of prey on the surface. In particular, Florida harvester ants struck with sand were observed to move towards the submerged larvae. Harvester ants are frequent cohabitants of the areas where V. americana hunt, and likely serve as occasional prey items.
This author observed a new surface behavior in larval V. americana that does not have an analog in pit builders. In the presence of prey, a larva will expose its entire head from the sand and hold it still with jaws closed and antennae upright (Fig. 1). This pose is reminiscent of the behavior called “spyhopping,” in which an aquatic animal orients its entire body vertically to poke its head out of the water. Cetaceans use this behavior to observe prey or objects above the surface, and it is likened to a human being treading water (Mohamed 2014). It is hypothesized that spyhopping in V. americana allows the animal to access information above the surface of sand without exposing the entire body. Partially exiting the substrate may expand the sensitive region of the stalked stemmata and antennae. The acuity of larval V. americana vision is not known, but on multiple occasions resting individuals (jaws open and buried) have been seen vibrating the body in such a way as to expose the stemmata and antennae, so evidently they are of some use. This action produces a distinctive image: a horizontal groove is formed by sand resting on the jaws, and the stemmata can be seen as black pinpricks within this groove.
Further investigation into the sensory capabilities of V. americana out of sand could support this hypothesis or suggest alternative functions for the behaviors. Investigating the sensory capabilities of a partially submerged V. americana would make for an interesting research subject in the future, as larvae unbury themselves completely in order to escape a shallow collection of sand. In conclusion, more study is necessary to determine the sensory capabilities of V. americana.
I am grateful to Dr. Mark Deyrup and Dr. John Oswald for assistance in locating wild V. americana and suggesting methods of study, and to the staff at Archbold Biological Station for making my stay so easy and wonderful. I thank my peers and my future peers at Cornell and Archbold, who shared and furthered my enthusiasm for these interesting creatures.