Interactions Between the Chilean Recluse Spider (Araneae: Sicariidae) and an Araneophagic Spitting Spider (Araneae: Scytodidae)
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Journal of Medical Entomology Advance Access published February 2, 2015 ARTHROPOD/HOST INTERACTION,IMMUNITY Interactions Between the Chilean Recluse Spider (Araneae: Sicariidae) and an Araneophagic Spitting Spider (Araneae: Scytodidae) 1,2,3 4 4 MAURICIO CANALS, NICOLA´ S ARRIAGADA, AND RIGOBERTO SOLI´S J. Med. Entomol. 1–8 (2015); DOI: 10.1093/jme/tju021 ABSTRACT In Chile, all necrotic arachnidism is attributed to the Chilean recluse spider, Loxosceles laeta Nicolet, a species that shares the microenvironmental habitats with the spitting spider Scytodes globula Nicolet. The latter species has been proposed as a potential predator of L. laeta. For this re- search, we studied the interaction between both species during individual encounters to assess the possi- bility of population regulation of L. laeta cohorts exposed to this potential predator. We found that in most encounters S. globula prevailed. Also, S. globula preys on spiderlings of L. laeta, with a population effect on cohorts of this species. These findings suggest that S. globula may be influencing L. laeta populations in central Chile. The population regulation of L. laeta by predation would be important because this species, in the absence of predators, has a high reproductive rate, and it can maintain populations of large size. However according to our results, although S. globula may aid in the reduction of both spiderling and adult L. laeta populations, and perhaps other Loxosceles species, it is insufficient for biological control of Loxosceles species. Its presence together with other control measures such as hygiene of the rooms can help to decrease loxoscelism incidence. KEY WORDS Loxosceles laeta, Scytodes globula, spider predation, loxoscelism Introduction L. laeta is a solitary spider of domestic habitats, found within households usually in dark corners, cracks, closets, Loxoscelism is a health problem caused by the bite of clothing, and bath towels, but sometimes can be found spiders of the genus Loxosceles (Araneae: Sicariidae). outdoors. Its activity is preferentially nocturnal; high tem- The cases in Chile are attributed to Loxosceles laeta peratures are a factor that favors its development (Sche- (Nicolet), Loxosceles gaucho Gertsch in Argentina, none and Letonja 1975; Schenone 1998, 2003, 2004; Loxosceles intermedia Mello-Leita˜o in Brazil, Schenone et al. 2001). With respect to diet, in Chile it Loxosceles reclusa Gertsch and Mulaik in the United has been reported that this spider feeds on flies, moths, States, and Loxosceles rufescens (Dufour) in Mediterra- and other small arthropods (LeviandSpielman1964; nean areas (Gertsch 1967, Gertsch and Ennik 1983, Schenone et al. 1970, 1989, 2001; Schenone 1998, 2003, Reyes et al. 1991, Vetter 2008). In Chile, all necrotic arachnidism is attributed to the 2004; Parra et al. 2002). From the medical point of view, Chilean recluse spider, L. laeta, a species that may be the epidemiology of loxoscelism incidents coincides with preyed upon by the spitting spider Scytodes globula nocturnal activity. Epidemiology also suggests larger spi- Nicolet (Araneae: Scytodidae). The biology of these der populations and greater activity during the summer two species is not well known (Fernandez et al. 2002; (Schenone 1998, 2003, 2004; Schenone et al. 2001). Canals et al. 2004, 2008; Canals and Solı´s 2013, 2014; A potential predator of L. laeta in Chile is the solitary Taucare-Rı´os et al. 2013). species, S. globula, a member of a group of spiders known as spitting spiders with recognized araneophagic habits (GilbertandRayor1985, Bowden 1991). The Scytodes spiders feed on spiders and insects such as Diptera, Lepidoptera, and Mantodea, avoiding schlero- 1 Programa de Salud Ambiental, Instituto de Salud Poblacional, tized and aggressive prey (Fernandez et al. 2002). Escuela de Salud Pu´blica Salvador Allende G., Santiago, Chile. During predation these spiders spit an adhesive 2 Departamento de Medicina, Facultad de Medicina, Universidad de substance through their chelicerae, immobilizing their Chile, Santiago, Chile. CP: 8380413 and Departamento de Zoologı´a; Facultad de Ciencias Naturales y Oceanogra´ficas, Universidad de prey (Foelix 1996, Araujo et al. 2008). These spiders are Concepcio´n, Concepcio´n, Chile. active during twilight and night and their thermal pref- 3 Corresponding author, e-mail: [email protected]. erences and desiccation tolerances are similar to those 4 Departamento de Ciencias Biolo´gicas Animales, Facultad de Cien- cias Veterinarias y Pecuarias, Universidad de Chile, Santiago, CP: of L. laeta (Alfaro et al. 2013, Canals et al. 2013). 8820808 Chile. S. globula is distributed in South America in Chile, VC The Author 2015. Published by Oxford University Press on behalf of the Entomological Society of America. For Permissions, please e-mail: [email protected] 2JOURNAL OF MEDICAL ENTOMOLOGY Bolivia, Argentina, Brazil, and Uruguay. Like L. laeta, L:D cycle, where they were maintained for at least 7 d. this species is common in human dwellings and gardens This allowed experimental trials to be conducted dur- of houses of central Chile (Fernandez et al. 2002). ing the day, but in the scotophase of the spiders. While there are references that suggest predation on Thirty-two interspecific encounters were performed in L. laeta by S. globula, there are few studies that support sealed circular plastic containers (diameter 19.5 cm; this (Fernandez et al. 2002, Canals and Solı´s 2013). depth 7 cm). The encounters were recorded with a high For example, Ramires (1999) and Ades and Ramı´res resolution digital video camera (SONY HDR-CX 700, (2002) documented the results of encounters between Chicago, USA), with night shot, in WAV format. The S. globula and three species of Loxosceles: L. laeta, rivals in each encounter were randomly chosen. They L. gaucho,andL. intermedia. These authors reported were sexed, and their body mass was measured with an that within 30 min of introduction, virtually all L. laeta analytic balance Shimadzu (AUX 220, Japan; 6 1mg). were alive, although they were victims of the adhesive The capture and the manipulation of individuals were substance and wrapped in silk lines. Of the 22 preda- performed by using brushes, anatomic tweezers, and tion events recorded, on three occasions the defense of rubber gloves, avoiding direct contact with the spiders. L. laeta caused leg autotomy in S. globula and, in two First, the resident spider was introduced in the instances, it was L. laeta which preyed on S. globula. experimental arena and was maintained for 1 wk Knowing that the activity rhythms, thermal prefer- for habituation before the encounter. Thirty-two ences, and tolerance to desiccation of these species are individuals of L. laeta (66.21 6 90.30 mg) and 32 indi- similar, it is necessary to describe the direct interaction viduals of S. globula (76.33 6 23.87 mg), with a body that occurs when these species meet (Hertz et al. 1993, mass ratio R ¼ mass of S. globula /massof Angilletta et al. 2002). If an encounter between L. laeta L. laeta ¼ 0.607 6 0.448, were used in the encounters. and S. globula is produced, we need to know the out- Sixteen individuals of L. laeta (Ll) were male come of the interaction between these species both at (mb ¼ 105.21 6 48.75 mg) and 16 female (mb ¼ the individual level (predatory acts) and population 238.82 6 66.14 mg), and 18 individuals of S. globula level (ability to regulate the population) in order to de- (Sg) were male (mb ¼ 71.17 6 21.68 mg) and 14 female termine if S. globula can be an effective biological con- (mb ¼ 82.80 6 24.76 mg). The encounters were distrib- trol agent (Wiedenmann 2000). uted in the following form: 7 Sg?-Ll?,11Sg?-Ll/,9 In this study, we analyzed the interaction between Sg/-Ll?, and 5 Sg/-Ll/. In 16 of the 32 encounters, S. globula and L. laeta during individual meetings and S. globula was the resident spider and in 16 it was the the possibility of population regulation of cohorts of intruder. At the beginning of the encounter, the new L. laeta exposed to this potential predator, with the fol- individual was introduced at 10 cm from the resident lowing working hypotheses: 1) as there is some experi- spider. The experimental trials lasted at least 60 min, mental evidence that suggests predation of L. laeta by ending when one spider killed and sucked its prey at S. globula, we propose that the most common response least for 20 min. In case when both were alive at the in individual meetings of the two species will be the end of 60 min, the experiment lasted another 60 min. If death of L. laeta; 2) as there is some experimental evi- neither were attacked or killed, the encounter was con- dence that suggests predation of L. laeta by S. globula, sidered a draw. we propose that this species has the potential to regu- In the videos, the frequency and the sequence of the late populations of L. laeta. behavioral events during spider interactions were recorded and analyzed, where an aggressive encounter was defined as physical contact between the spiders, resulting in the death of one spider. The description Materials and Methods and nomenclature of behavioral events followed Gilbert Individual Interactions. Forty sexually differenti- and Rayor (1985) and Ferna´ndez et al. (2002) for the ated individuals of L. laeta and S. globula were col- construction of the ethogram. The 10 behavioral events lected inside institutional storehouses and inside considered were—1) Alert posture, 2) Leg retraction, human dwellings in the cities Santiago and Valparaiso 3) Tapping, 4) Prey palpation, 5) Spitting, 6) Scraping in Chile between December 2012 and December (reciprocal rasping of pedipalps and cutting the threads 2013. Sexual differentiation can be recognized from 5th of the web), 7) Reach (prey capture), 8) Roll (envelop- and from 6th moult in S.