Substrate moisture,particle size and temperature preferences of trap‐building larvae of sympatric antlions and wormlions from the rainforest of Borneo

1. Larvae of antlions (Neuroptera: Myrmeleontidae) and wormlions (Diptera: Vermileonidae) display a convergently evolved sit‐and‐wait hunting strategy of building pitfall traps in sandy areas. This study investigated a sympatric population of antlions and wormlions in the lowland rainforest of Borneo for substrate moisture, particle size and temperature preferences. It was hypothesised that these animals would show different preferences regarding these microhabitat traits. 2. The results showed that antlions had a higher aversion to moisture compared with wormlions, but that wormlions had a higher preference for small‐particle sand. Furthermore, thermal preferences in antlions and wormlions were significantly different, with antlions choosing higher temperatures. 3. The detected differences between antlions and wormlions might contribute to their niche partitioning in the mixed Bornean population and thus facilitate coexistence of these animals. It is possible that the hotter and dryer microhabitat edges are preferred by antlions.     

Substrate particle size affects pit building decision and pit size in the antlion larvae Euroleon nostras (Neuroptera: Myrmeleontidae)

Abstract. The larvae of the antlion Euroleon nostras are pit-builders, constructing pitfall traps in loose sand. The number of pits and the pit diameter are recorded when larvae are kept in substrates with different particle sizes. The most convenient pit-building sand fractions are two fractions with fine sand (≤ 0.23 mm; 0.23–0.54 mm). The largest pits are constructed in sand with a particle size of 0.23–0.54 mm. In this sand fraction, larvae of all three instars most readily build pits. No pits are constructed in sand with a particle size greater than 1.54 mm. First- and second-instar larvae avoid building pits in substrates of particle size 1–1.54 mm, but third-instar larvae construct pits in this sand fraction. It is assumed that the antlion is capable of distinguishing between substrate types and this hypothesis is tested by giving larvae the choice of building a pit in one of four particle-size fractions. Larvae of all three instars prefer to build pits in the fraction with a particle size of 0.23–0.54 mm. Only third-instar larvae build pits in all four fractions, but only occasionally in the coarser fraction.     

The effects of starvation and repeated disturbance on mass loss,pit construction,and spatial pattern in a trap‐building predator

1. Starvation tolerance is an important trait for animals, as most will encounter starvation within their lifetime. Sit‐and‐wait predators are better adapted to starvation owing to their naturally low encounter rate with prey. 2. Starvation tolerance was studied under three levels of disturbance of wormlion larvae, a strict sit‐and‐wait predator that constructs pits. 3. Frequently disturbed wormlions constructed pits less often, and larger individuals continued to construct pits more frequently than smaller ones. It was expected that a high disturbance level would lead to a high rate of mass loss, however, surprisingly, the rate of mass loss was not higher for the frequently disturbed group. This suggests that the energetic cost of pit construction and maintenance is not as high as previously suggested for other pit‐building predators. 4. Larger individuals tolerated starvation better, in losing a lower proportion of their initial body mass and having higher chances of survival throughout the experiment. 5. The effect of starvation on the distance to neighbours was also investigated, and starved individuals were expected to maximise this distance in order to avoid interference competition. However, wormlions were usually clumped, and starvation or feeding had no effect on the pits' spatial pattern, suggesting that interference competition plays a minor role in this species. 6. Generally, wormlion larvae demonstrated a high starvation tolerance and low mortality rates even after 9 weeks of starvation.     

Effects of larval antlions Euroleon nostras (Neuroptera, Myrmeleontidae) and their pits on the escape-time of ants

Abstract. Pit-building antlions are predators with a unique predation strategy, namely using pitfall traps constructed in loose sand to catch prey. Here, prey escape-time in the field is measured by introducing ants into one of four different treatment arenas. The first treatment lacks pits and antlions, the second includes 10 antlions that did not build pits, the third comprises eight artificially constructed pits, and the fourth is a treatment of eight antlions in pits and two without pits. Their pits are of a similar size to those used in the third treatment. When antlions are present without constructing pits, they impede the dispersal of prey. The mean escape-time for one half of the released ants is twice as long with antlions present as without them. When pits are present, the time taken for one half of the released ants to escape the predator is more than 10 times as long as when pits are absent. Escape-time from artificial pits is three times that from nonpit building antlions. Pits hinder the escape of ants and therefore increase the amount of time that the prey is available for capture. In the area where the pits are occupied by antlions, escape-time is four times longer than in a treatment with similar sized artificial pits. Thus, it appears that not only a pit, but also the presence of antlions influences the capture success.     

First record of the genus Bankisus Navás, 1912 in China, with the description of a new species (Neuroptera, Myrmeleontidae)

A new species of Bankisus Navás, 1912,(Bankisus sparsussp. n.)is described and illustrated with the genus newly recorded from China. A key to species of Bankisus is provided.     

Habitat preference of wormlions and their behavioural repeatability under illumination/shade conditions

1. Animal personality is defined as the repeatable between‐individual differences in behaviour over time and contexts. Some personality traits, such as activity or aggression, have received much attention while other behaviours, such as habitat preference or learning, have been neglected. 2. Wormlion larvae are sit‐and‐wait dipteran predators that inhabit shaded microhabitats in the field and also prefer shade in the laboratory. The aim of the present study was to examine wormlion larvae behavioural repeatability in general and specifically in the context of habitat preference. In order to achieve this, three experiments were conducted to determine whether, to what extent and under which conditions wormlion preference for shaded microhabitats is repeatable. 3. Individual tendency to relocate when the environment conditions deteriorate was also assessed, by switching between shaded and illuminated conditions, either with or without pit destruction. 4. Larvae showed a highly repeatable preference for shade. Repeatability was detected in additional behavioural traits: pit construction, pit area and tendency to relocate. 5. This behavioural repeatability was demonstrated under constant microhabitat conditions, with distinct behaviours in each setting. Under constant illumination, wormlions constructed smaller pits, moved over longer distances and were found at the tray edges more frequently than under constant shade conditions, suggesting that illuminated environments are perceived as risky or unsuitable. 6. Switching between the two microhabitat conditions without pit destruction induced fewer relocations than switching with pit destruction, suggesting that wormlions do not tend to abandon their pits, even if their microhabitat conditions deteriorate.     

Sand as a medium for transmission of vibratory signals of prey in antlions Euroleon nostras (Neuroptera: Myrmeleontidae)

Abstract.  European pit-building antlions ( Euroleon nostras / Geoffroy in Fourcroy/) detect their prey by sensing the vibrations that prey generate during locomotory activity. The behavioural reactions and some of the physical properties of substrate vibrations in sand are measured to observe signal transmission through the substrate. The frequency range of the signals of four arthropod species ( Tenebrio molitor , Pyrrhocoris apterus , Formica sp. and Trachelipus rathkei ) is 0.1–4.5 kHz and acceleration values are in the range 400 μm s⁻² to 1.5 mm s⁻². Substrate particle size and the frequency of prey signals both influence the propagation properties of vibratory signals. The damping coefficient at a frequency 300 Hz varies from 0.26 to 2.61 dB cm⁻¹ and is inversely proportional to the size of the sand particle. The damping coefficient is positively correlated with the frequency of the pulses. Vibrations in finer sand are attenuated more strongly than in coarser sand and, consequently, an antlion detects its prey only at a short distance. The reaction distance is defined as the distance of the prey from the centre of the pit when the antlion begins tossing sand as a reaction to the presence of prey. The mean reaction distance is 3.3 cm in the finest sand (particle size ≤ 0.23 mm) and 12.3 cm in coarser sand (particle size 1–1.54 mm). The most convenient sands for prey detection are considered to be medium particle-sized sands.     

Prey detection in antlions: propagation of vibrational signals deep into the sand

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 (α₁₀) 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.     

Different predation efficiencies of trap‐building larvae of sympatric antlions and wormlions from the rainforest of Borneo

1. This study reports the discovery of sympatric populations of antlions (Neuroptera: Myrmeleontidae) and wormlions (Diptera: Vermileonidae) in a unique system of sandy microhabitats in the lowland rainforest of Borneo. The two species convergently evolved sit‐and‐wait predatory larvae, which construct pitfall traps to hunt insects. Despite similar specialised foraging strategies, the two species coexist in the competitive environment of small, isolated sandy patches in the rainforest, which begs the question: what biological characteristics allow their coexistence? 2. Based on larval morphology alone, it was predicted that antlions would build larger traps, which would allow them to efficiently hunt larger prey. Addressing this hypothesis, this study compared the volumes of traps constructed by the two species under field and laboratory conditions. A laboratory experiment compared their efficiency of capture of three ant species that differed in body size. 3. The results show that antlions constructed larger traps and captured prey more efficiently. The difference between the species could not be explained by trap size alone. The findings demonstrate that the overlap in resource use in these two species was low, and it is suggested that there is a separation in prey utility between them, allowing their coexistence in the space‐limited habitat of the tropical rainforest.