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

Abstract

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.

Past thermal conditions affect hunting behaviour in larval antlions

“…In another group of trap builders, wormlions (Diptera: Vermileonidae), which represent an example of convergent evolution with antlions and sometimes even occur in sympatry [ 46 , 47 ], the effects of experience of various kinds are complex. For example, starvation periods sometimes increase the neighbouring distance in these dipterans but sometimes not, depending on other factors [ 48 , 49 ]. Abiotic conditions, such as previous medium quality or light exposure, most likely have little effect on the behaviours of wormlions [ 50 – 52 ].…”

The effect of fasting and body reserves on cold tolerance in 2 pit-building insect predators

“…Although the morphology of each species is strikingly different (see Figure 1 in the Supplementary Material ), their pits are almost indistinguishable. Other similarities include a high starvation tolerance (typical of any sit-and-wait predator; Scharf and Ovadia 2006 ; Scharf and Dor 2015 ) and an active process of habitat choice based on abiotic factors, such as substrate type ( Devetak and Arnett 2015 ). However, whereas antlions are cannibals ( Barkae et al.…”

“…This insect is very common in cities, inhabiting the thin loose soil layer below buildings ( Dor et al. 2014 ; Scharf and Dor 2015 ). The larval stage in both species is long (at least a year), and the adults are weak-flying and short-lived.…”

“…A starvation period of 21 days was chosen because it induces behavioral changes in antlions (such as pit relocation and response time to prey; Hauber 1999 ; Scharf et al. 2010 ; reviewed in Scharf and Ovadia 2006 ) and significant mass loss in wormlions ( Scharf and Dor 2015 ). On the other hand, it is not a too harsh stress, which would lead to drastic physiological changes or mortality.…”

Digging the optimum pit: antlions, spirals and spontaneous stratification

“…Hedgerow bottoms are full of debris and we reasoned that antlion larvae should have the ability to choose places for pit excavation which are relatively free of debris such as plant roots, fallen twigs and leaves. Indeed, antlion larvae do seem skilfully to choose sites where they have adequate space for their pits [42,43]. Hence, antlion larvae should centre their pits in suitable places provided for them.…”