Morphology and behaviour of third instar larvae of the Holomediterranean antlion species Myrmecaelurus trigrammus (Pallas) are described. Larvae are facultative pit-builders, they either ambush their prey at the surface, or dig pitfall traps that prey fall in to. Dark brown spots on dorsal and ventral sides of the head and on dorsal side of the thorax are characteristic of the larvae. Eye tubercles are not prominent. Jaws are equipped with long bristles, campaniform sensilla, sensilla coeloconica, and digitiform sensilla. A unique feature is the shape of the tips of all three teeth that is screw-like with a polyhedral surface. The body surface is covered with longitudinally grooved bristles and plumose hairs. On the tip of the antennae and on terminal and subterminal parts of labial palps sensilla basiconica occur. On the 9th abdominal segment there are two bulges, each of them bearing four digging bristles. Non-prominent eye tubercles and numerous mandibular bristles are morphological traits of pit-builders. Most of the behavioural traits are related to pit builders, whereas forward movement, waiting for prey without a pit and frequent changing of ambush location are traits of non-pit builders.

Behavioral plasticity allows animals to maximize their fitness in a variety of environmental conditions. Trap‐building predators represent case studies in such plasticity as the characteristics of their traps are dependent upon the substrate available. We investigated the effect of sand particle size on pit construction in antlions (Euroleon nostras), sand‐dwelling insect larvae that build pitfall traps to capture prey. The pit construction behavior of the species comprises six stages. When antlions were exposed to different sand particle sizes, their behavior differed in terms of the occurrence and duration of particular stages and in the frequency of jerks produced during sand tossing. Jerk frequency was negatively correlated with sand particle size and also changed during pit construction. Furthermore, at larger particle sizes, individuals occasionally constructed irregular traps with a figure of eight shape, and they crossed the center of the truncated cone during deepening. In the largest substrate, particle size of antlions did not construct pits. Our results demonstrate that variation in traps under differing environmental conditions stems directly from behavioral plasticity in this species.

Temperature is of crucial importance, affecting all aspects of insect life such as survival, development and daily activity patterns, and consequently behaviour. In the present study we evaluated the effect of temperature on the behavioural plasticity of antlion larvae, the sit-and-wait predators, which are considerably more dependent on local habitat conditions. We provided ethological descriptions of pit construction and feeding behaviour. An increase in temperature led to greater activity and consequently to greater frequency of sand tossing during pit construction. Larvae constructed bigger pits at higher temperatures, but required less time than at lower temperatures, when the resulting pits were the smallest. At low temperature, larvae required more time for feeding, and behaviour followed a core pattern with little variety, in comparison to behaviour at high temperatures. Two behavioural patterns occurred only at the highest temperature: ‘relocation’ and ‘submergence’, presumably in response to high temperatures.

Trap-building antlion larvae detect their prey according to the substrate vibrations produced during movement of the prey on the sand surface. Although most studies are devoted to surface vibrational waves, in the present study, we determine the role of vibrations travelling through deeper sand layers. A behavioural experiment confirms that vibrational stimuli from prey insects on the surface of the sand stimulate the antlions buried in deeper sand layers to move towards the surface. Sand depth and particle size both have a strong effect on signal transmission. The damping coefficient (α 10 ) varies from 0.49 dB to 3.30 dB cm −1 and depends on frequency (in the range from 100 to 300 Hz), particle size (from finest to coarse sand) and distance from the source of the vibrations. The deeper the sand, the narrower the frequency range of the signal becomes. Sand is a filter for higher frequencies. The smaller the sand particles, the more intense the filtering becomes. Fine sand with a mean sand particle size of 360 μm is a more efficient filter than coarse sand; consequently, high frequencies (> 2.5 kHz) are eliminated at a depth of 3 cm. Mean frequency depends on both depth and particle size. However, low frequency signals still propagate at a certain distance, which is biologically important in prey detection. Although the most efficient signal propagation appears to occur in coarse sand, it contains overly large particles that are inconvenient for relatively small antlion larvae. Predators seek a compromise between fine and coarse sand choosing medium sand.

The study focused on the behaviour of sit-and-wait antlion larvae in interspecific interactions. Antlion larvae usually occur in clusters with a high density of individuals; therefore, competition can be intense. We observed two abundant antlion species, E. nostras and M. formicarius, which co-occur in some habitats. In a simple habitat choice experiment where substrates differed according to sand particle size, we found that E. nostras exhibited dominance over M. formicarius. Most E. nostras larvae remained in the more suitable substrate and constructed pits, while all the M. formicarius larvae moved out of the suitable area, and did not build pits. In the second experiment, we observed the characteristics of the pit-fall traps and scored the occurrence of larval relocation in relation to interactions and in the control group, where larvae were kept in containers separately. In interactions, the larvae of E. nostras constructed smaller pits, but pit enlargement was greater in comparison to the control group. M. formicarius larvae constructed similar sized pits in both groups; however, enlargement was greater in the control group. Relocation of larvae occurred only during interactions. In direct interactions, we found 15 behavioural patterns, which are described in detail for the first time. In the presence of a competitor, larvae showed intense territorial behaviour. We recorded several behavioural patterns during larval confrontation, and interestingly, intraguild predation rarely occurred. In most cases, E. nostras larvae outcompete M. formicarius, which was evident from the larger pits and the rate of pit-construction.