Massive spider web aggregations in South American grasslands after flooding

Abstract

1. Major floods of riparian and grassland habitats may lead to a shift in the availability of resources (e.g., food, space) that produces cascading effects on the organisms that rely on it. After flooding occurs, particularly in natural grasslands or agricultural fields, massive aggregative spider webs are occasionally observed. However, given it is an infrequent and unpredictable event, it is seldom reported in detail.2. We characterise two instances of massive web aggregations that followed major floods in grasslands and agricultural fields in Argentina and Uruguay in 2015. In the Argentinean event, we compare the composition of spider assemblages on the webs, in grasses below the webs, and in grasses from nearby habitats, with samples taken in the same location but when the fields were not flooded.3. The assemblage of spiders in the massive web aggregations largely consisted of immature Diapontia uruguayensis (Lycosidae). In the grass below the webs, we recorded an impressive density of 1007 specimens m−1 belonging to several spider species, 6–15 times the density of similar samples without aggregated webs, co‐occurring and showing low levels of aggression among them.4. Our observations and review of the literature support the idea massive webs produced by lycosids are a byproduct of an unusually high density of spiders simultaneously attempting to disperse through the air via ballooning and escaping from floods.

Should I stay or should I fly: Aerial dispersal in a funnel‐web wolf spider from the grasslands of southern South America

“…Although at the family level we could expect the existence of aerial dispersal, little is known about the dispersal capacity of the species in this particular subfamily. Researchers have observed aerial dispersal from tip‐toeing behaviour during floods in species of the genus Diapontia (Piacentini et al., 2017, 2021), a member of this subfamily with an apparent lower dependence on web‐based life compared to A. lagotis (N. Kacevas & M. González, pers. obs.).…”

Discovery and Genetic Characterization of Single Cohort Adult Colonies With Male Aggregations, and Preliminary Evidence for Lekking in a Malagasy Kite Spider (Isoxya, Gasteracanthinae)

“…Although nearly all spider species live solitarily from early spiderling state, conspecific grouping of spiders do occur. These may be in the form of aggregations of multiple species at various life stages around suddenly abundant resources (Greene et al 2010, Piacentini et al 2021), but more commonly colonies involve spiders that are facultatively or obligatorily group living (Avilés 1997, Bilde and Lubin 2011). Even among species in the latter category, the colonies found in Isoxya manangona are clearly, in some respects, unique among spiders.…”

“…When and if they aggregate, temporary swarms form surrounding an abundant resource. This may occur in man-altered habitats or buildings (Greene et al 2010), or following natural events such as flooding (Piacentini et al 2021) when large irregular multi-species and multi-cohort ‘colonies’ can form temporarily as insect populations boom. Unlike most species, obligate social spiders like Anelosimus eximius (Keyserling, 1884) and other highly social species cooperate in web building, prey capture, and maternal care (Avilés 1997, Marques et al 1998, Agnarsson 2006, Yip and Rayor 2014).…”

Spatial aggregation of herbivores and predators enhances tri‐trophic cascades in paddy fields: Rice monoculture versus rice‐fish co‐culture

“…Aggregation pheromones of predators not only facilitate predator aggregation but also affect prey performance (Aflitto & Thaler, 2020; Jacobsen et al, 2016). Web‐weaving spiders might use pheromones to aggregate to increase encounter rates of conspecific individuals (Piacentini et al, 2021) as they likely acquire fitness benefits from aggregating with conspecifics (Fitzgerald & Ives, 2017). However, conspecific aggregation may also increase cannibalism and interference competition (Lesne et al, 2016).…”