Araneae

Berx, Peter, Bosmans, Bart, Dekoninck, Wouter, Janssen, Marc, Stassen, Eugène & Crevecoeur, Luc, 2023, Faunistic survey of myrmecophilous and other ant-associated beetles and spiders in the Belgian province of Limburg (Araneae, Coleoptera, Hymenoptera: Formicidae), Belgian Journal of Entomology 141, pp. 1-61 : 47-48

Araneae

Despite their ubiquity, ants are not the main prey of spiders due to the aggressive behaviour these social insects generally display towards other arthropods. From our large-scale survey we selected six myrmecophagous spiders, described in the literature in association with ants. Of these six spiders Acartauchenius scurilis and Mastigusa arietina received the status endangered in Belgium, Thyreosthenius biovatus is labeled critical and Zodarium rubidum is noticed as a species with rare geographically restrictions ( MAELFAIT et al., 1998). With only sporadic reports of T. biovatus ( Table 38), the status of this species is considered critical to which Thomas Parmentier countered that a close monitoring of the mounds of the red wood ants, shows that this spider has probably a much wider distribution ( PARMENTIER et al., 2015).

To indicate the possible relationship between the spiders and ants, we selected from our field observations these data where both groups were found in the same trap, emphasising that 88% were pitfall traps ( Table 39). Within the range of action of the foraging spiders and ants, this shows occupancy of both groups within the same restricted circumference. In our table ( Table 39), we have marked the winged females and males in red because their dispersal behaviour during the nuptial flight may fall outside the action radius of the workers. These observations also teach us that the ant-mimicking spider Myrmarachne formicaria is not only the most common species of this selection but also a generalist in terms of its association with ants ( Table 38 & 39).

The preference for ants as prey has been experimentally demonstrated in the zodariid spider Zodarion rubidium , of which the female is 3.5–4.5 mm in size and with a light orange cephalothorax and legs, contrasting with a dark sepia abdomen resembles the myrmicid ants such a s M. sabuleti . In an experimental setup, ants from the genera Camponotus Mayr, 1861 , Formica Linnaeus, 1758 , Lasius Fabricius, 1804 , Monomorium Mayr, 1855 , Myrmica Latreille, 1804 , Plagiolepis Mayr, 1861 , Solenopsis Westwood, 1840 , Tapinoma Foerster, 1850 and Tetramorium Mayr, 1855 , were offered as food. In addition, the spiders also gained access to other invertebrates such as termites, beetles, aphids, silverfish, flies, crickets, and grasshoppers. Except for the termites, only ants were consumed, a preference that the researcher was also able to establish in the field ( PEKÁR, 2004). All Zodarion spp. are defined as obligate myrmecophages and the researchers go so far as to state that without the food supply of ants, these species would not survive ( CUSHING, 2012).

In the 22 investigated UTM grids where Z. rubidum was collected with pitfall traps, the two ant species that are the main food source( PEKÁR & KŘÁl, 2002), L. platythorax (sampled in 17 joined grids) and T. caespitum (sampled in 16 joined grids) were also present. In their discussion of Z. rubidium, PekÁr and KrÁl strongly emphasize the morphological similarity with M. sabuleti and argue that the range of this spider matches that of M. sabuleti ( PEKÁR & KŘÁL, 2002) . During our survey, M. sabuleti was found in 20 of the 34 pitfall traps in which Z. rubidum was caught but this number was exceeded by T. caespitum with 22 observations. In aggressive contact with the ants, Z. rubidum will avoid confrontation by tapping the ant’s antennae with its first pair of legs and protruding an already captured prey in front of it ( PEKÁR & KŘÁL, 2002). Probably all Zodarion spp. have a femoral organ, an external structure of modified hairs situated at the distal tip of the femora combined with an exocrine gland. The researchers are speculating about the role of the secretion of the gland, but it might be a volatile substance to subdue attacking ants ( PEKÁR & ŠOBOTNÍK, 2007).

Together with L. brunneus and T. nylanderi , we collected the endangered Mastigusa arietina in the municipality Houthalen (FS7353) by sieving wood dust from a hollow beech ( Table 39). Moreover, this spider was also observed in the nests of L. flavus and L. niger ( BONTE et al., 2000) and during surveys in northwest Belgium, the species was collected in two nests of L. fuliginosus and in one nest of T. caespitum ( PARMENTIER et al., 2022) .