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.
Co-occurring species often compete with each other directly and indirectly. Intra-guild predation (IGP) is an extreme manifestation of direct competition, which involves the attack, killing and eating of potential competitors. We studied the competitive interactions between two pit-building antlion species that co-occur in the Israeli desert: Myrmeleon hyalinus residing in the more productive sandy soil, and Cueta lineosa solely inhabiting poorer loess soils. To understand the mechanisms driving C. lineosa away from the more productive habitat, we explored the factors triggering IGP of one antlion species on the other. We tested whether IGP is affected by soil type, depth and temperature. IGP was asymmetrical with M. hyalinus preying on C. lineosa, and it intensified as the size difference favoring the former increased. Interactive rather than additive effects governed IGP, which was lowest in sandy soil combined with low temperature, and highest in shallow loess soil. C. lineosa possesses a smaller head and thorax relative to its abdomen compared to M. hyalinus, providing a possible explanation for the advantage of M. hyalinus in direct competition. We then focused on the weaker competitor, C. lineosa, examining how it copes with competition induced by M. hyalinus. Both the growth and survival rates of C. lineosa declined in the presence of M. hyalinus. The asymmetrical IGP C. lineosa experiences from M. hyalinus combined with its competitive inferiority may explain why it is mostly found in poor habitats, while its intra-guild competitor is abundant in the more productive habitats.
Traps are rarely used by animals, despite the plausible benefits of broadening the number and diversity of prey that sit-and-wait foragers might be able to capture. The most well-known trap building sit-and-wait foragers are among the invertebrates, i.e. antlions, wormlions, glow worms, caddisflies, and spiders. A plausible hypothesis for the paucity of trap building by other animals is that biomechanical limitations render them inefficient or ineffective at catching sufficient prey. Here I examined the literature to make a valued judgement about the validity of this hypothesis. It appears that antlion and wormlion pit traps cannot catch and retain the largest prey they might expect to encounter. Arachnacampa glowworm traps are functionally efficient, facilitated by the animal’s bioluminescence. Nevertheless they only function in very moist or humid conditions. Caddisfly traps rely on flowing water to be able to capture their prey. Spiders are exceptional in developing a wide range of prey trapping strategies, from webs with dry adhesives, to sticky orb webs, to modified orb webs, e.g. elongated “ladder” webs, to webs with additional structures, and web aggregations. Some spiders have even redesigned their webs to minimize the high prey escape rates associated with web two dimensionality. These webs nevertheless are constructed and used at specific costs. While hard data across all of the invertebrate predators is lacking, there seems to be credence in the hypothesis that the biomechanical limitations placed on trap functionality can explain their limited use among animals.
Some terrestrial leeches mate by entwining the anterior ends of their bodies and then copulating. Here, we report first observations of a similar behavioral pattern in Haemadipsa picta terrestrial leeches from Malaysian Borneo. However, because the observed pattern can be easily induced artificially with no clear evidence of copulation, we suggest that it may serve another function, particularly in H. picta. We hypothesize that the wrestling behavior, as we term it, may be a ritualized aggressive display driven by competition for ambush location. Haemadipsid fauna of the region is poorly studied, therefore our observations extend limited knowledge about these leeches and open interesting research avenues for the study of the wrestling behavior.
Carnivorous plants are pure sit-and-wait predators: they remain rooted to a single location and depend on the abundance and movement of their prey to obtain nutrients required for growth and reproduction. Yet carnivorous plants exhibit phenotypically plastic responses to prey availability that parallel those of non-carnivorous plants to changes in light levels or soil-nutrient concentrations. The latter have been considered to be foraging behaviors, but the former have not. Here, I review aspects of foraging theory that can be profitably applied to carnivorous plants considered as sit-and-wait predators. A discussion of different strategies by which carnivorous plants attract, capture, kill, and digest prey, and subsequently acquire nutrients from them suggests that optimal foraging theory can be applied to carnivorous plants as easily as it has been applied to animals. Carnivorous plants can vary their production, placement, and types of traps; switch between capturing nutrients from leaf-derived traps and roots; temporarily activate traps in response to external cues; or cease trap production altogether. Future research on foraging strategies by carnivorous plants will yield new insights into the physiology and ecology of what Darwin called “the most wonderful plants in the world”. At the same time, inclusion of carnivorous plants into models of animal foraging behavior could lead to the development of a more general and taxonomically inclusive foraging theory.
The remarkable diversity of antlions in the Afrotropical region is counterbalanced by the scarce knowledge of their biology and ecology. In particular, their larval stages are largely unknown and the morphology of African pit-building species was never investigated in detail. The larvae of three pit-building species attaining a wide distribution across the whole continent, namely Myrmeleon caliginosus, M. obscurus and M. quinquemaculatus are described, illustrated and compared with congeners for the first time. Moreover, M. caliginosus is reported for the first time from Namibia, notably extending the known range of this antlion, with implications on the taxonomy and the identification of African Myrmeleon species. The larvae of these three species highlight the overall conservative morphology across the whole genus, differing in relatively minor characters such as size, proportions, pattern and chaetotaxy.
When choosing among several potential habitats, animals should strive to choose the habitat that provides the highest fitness. When animals choose habitats that do not provide the best possible fitness, there is a mismatch between habitat preference and performance. A common reason is that of limited information or perceptual range. Sit-and-wait predators are particularly deficient in information, due to spending most of their time in ambushing prey and, when they do travel, they cover only short distances. Here, we studied the effect of placing pit-building wormlions at a short distance from their preferred microhabitats, on the likelihood of them choosing it. When placed on the border between deep and shallow sand, fine and coarse sand, or dry and wet sand, wormlions chose the former in each case in vast proportions. However, the ability of wormlions to recognize and/or choose favorable habitats decreased sharply with distance, suggesting that they are limited in their perceptual range. We next examined whether wormlions relocate their pits following a continuous disturbance arriving always from the same side. Although they did so, their movement direction was unrelated to the direction of the disturbance. The preference of wormlions for a favorable, shaded microhabitat depended greatly on the location of a conspecific competitor: the favorable microhabitat was more attractive for wormlions when a competitor was more distant from it than when the competitor was located on the border between the favorable and unfavorable microhabitats. Our findings support previous studies indicating the limited perceptual range of pit-building predators.
The physical structures built by animals are considered extended phenotypes that reflect how organisms make decisions and deal with changes in their biotic and abiotic environment. We summarize the results of several studies on Myrmeleon crudelis, a neuropteran larva that digs pit-traps in the soil to capture small arthropods (mostly ants) in the tropical dry forests of Costa Rica. Specifically, we showed how this species responds to varying biotic and abiotic conditions with changes in the design and/or location of its pit traps. Several experiments and field comparisons indicate that: 1) antlions adjust the pit design according to the abundance and type of prey. When prey is scarce, antlions increased trap diameter, an architectural adjustment that enhances the probability of prey encounter. Antlions that experienced high prey abundance, but the prey easily escaped, then increased pit depth, an adjustment that increases the chance of prey retention; 2) soil compaction strongly reduced pit-trap size and abundance; 3) antlions preferred soils with high proportion of fine-particle size to build pits. In fine-grained soil, pit-traps are larger and more efficient to capture prey than traps in coarse-grained soils; and 4) pit-traps may also be affected through indirect effects of soil structure and vegetation cover. Areas with fine-soil presented less plant cover, and plant cover could be beneficial for antlions because it acts as a shelter against direct sunlight and rainfall, or it may represent a cost because it is a source of leaflitter falling in the pits. The works summarized here how trap-building predators can exhibit considerable flexibility in trap construction in response to various biotic and abiotic factors, emphasizing how the study of extended phenotypes can be a useful approach to better understand the flexibility of foraging behaviors.
Predation is one of the main interactions between organisms and one of the primary selective agents for their survival. Both prey and predators have developed different strategies and characteristics that allow them to be conspicuous or go undetected. In sit and wait predators, their shape and appearance are important factors that allow them to remain undetected by their potential prey. Sit and wait predators such as crab spiders are difficult to identify when they sit on flowers or areas of flowers with colors similar to the color of their bodies. In this study, we aimed to determine if insects can recognize the morphology and color polymorphism of crab spiders by evaluating the response of flower visitors. We quantified the visits and approaches of floral visitors to the flowerheads of Palafoxia lindenii with spider morphology and color polymorphism treatments. Our results show that insects in general, and bees in particular, avoid visiting flowers with a real spider or a spider model and visit vacant flowers more frequently. In the case of the color polymorphism, insects approached flowerheads with spiders with a similar frequency independently of the color of the spiders, but did not visit them. Insects appeared to identify spiders through their morphological characteristics rather than their color characteristics, since flower visitors did not discriminate between the evaluated spider colors (white, lilac, and purple). This study emphasizes the differential response of different insect prey to the presence, color, and morphology of sit and wait predators.