Sun Spiders of the Family Mummuciidae and the Importance of Natural History Collections
Ricardo Botero-Trujillo, Ph.D.
Theodore Roosevelt Postdoctoral Research Fellow, Department of Invertebrate Zoology and Richard Gilder Graduate School, American Museum of Natural History, N.Y., U.S.A.
All of our readers surely know what a spider is. Loved by some, feared by others, they are found almost everywhere. Look carefully and you will find them living in your home or working place.
Spiders are the most famous order within the class, Arachnida, however, several other orders of arachnids exist. Some of them are reminiscent of spiders in certain aspects, whereas others have notably different appearances (for example, scorpions). In many languages, including English and Spanish, the word “spider” (or equivalent) is combined with other words that together refer to some of those other “spider-looking” arachnids. For example, the arachnid order Amblypygi is commonly referred to as whip spiders, while the lesser known arachnid order, Ricinulei, is called the hooded tick spiders, although neither of these orders are actually spiders.
For the Taxon of the Month, we focus on another arachnid order known as the sun spiders or camel spiders, but referred to in the scientific community as Solifugae. As you may have guessed, solifuges are not spiders (clearly not camels either). Most species in this >1100 species group are nocturnal (active at night). Therefore, the common name sun spider is only technically accurate for diurnal (active during the day) species (Cloudsley-Thompson 1977). One solifuge family that is active during the day is Mummuciidae (Figure 2). This is one out of 12 families of living solifuges, and one of only four present in the Americas (Maury 1984). Most Mummuciidae species are quite small, not surpassing 20 mm in total length although most individuals are much smaller than that! One species in this family, Vempironiella aguilari, described from Peru has the smallest males among all solifugaes with adult males not reaching 6 mm (Botero-Trujillo 2016). Despite their small size, mummuciids are ferocious and voracious animals, feeding on practically any prey that they can kill (Cloudsley-Thompson 1977).
Mummucids are entirely diurnal animals. They are quite abundant in open areas, and can be found during the hottest months of the year (Figure 2). They can barely be spotted when they are running, for they are extremely fast, especially males. In contrast, females are most often found digging burrows in the substrate, which they use for refuge and egg deposition. When studied under a stereomicroscope (or even when seen in Figure 1) members of Mummuciidae can very easily be recognized by the presence of three longitudinal dark bands on the dorsal surface. This coloration pattern is very unique among South American solifuges, and only reminiscent of some other diurnal species in the Old World (Botero-Trujillo 2018).
Like other Solifuges, mummuciids have very large chelicerae (jaws), which are among the largest and most powerful in Arachnida (Figure 3). Chelicerae are used to kill and tear apart prey, but also have other functions. Females use the chelicerae for digging burrows, whereas the chelicerae of males are morphologically and functionally modified to transfer sperm into females (Figure 4; Bird et al. 2015). For this reason, it is not surprising that males have developed taxon-specific morphologies for their chelicerae, and consequently, the chelicerae of males represent an extremely important structure for uncovering solifuge diversity (Bird et al. 2015; Botero-Trujillo et al. 2017). Despite their aggressiveness and high cheliceral strength relative to their body size, mummuciids, and solifuges in general, are harmless to humans. They lack venom, relying completely on speed and their strong chelicerae for hunting.
Another interesting fact about Mummuiciidae, and solifuges in general, is that despite being an arachnid and having eight legs, they actually only use six legs for walking (much like insects do; Punzo 1998). They use their first pair of legs as sensory appendages, raising them above the substrate, detecting cues, much like insect antennae (Figure 5). But that’s not all. The pedipalps (Figure 5), which have a common ancestry with scorpion “arms”, are also modified in solifuges. They are leg-like in appearance, serve a sensory function and have an adhesive structure, which is eversible, allowing them to literally climb on surfaces as smooth as glass, as well as capture jumping prey (Cushing et al. 2005; Klann et al. 2008; Willemart et al. 2011)!
Despite Mummuciidae being a widespread taxon in arid and semi-arid regions of most South American countries, little is known about this family. Very little information exists on the habitat requirements, diversity and reproduction of this family and no comprehensive examination of the group exists. For my Ph.D. research (Botero-Trujillo 2018), I studied the diversity of mummuciid solifuges, addressing their morphology, distribution, evolution, and classification at the Argentinean Museum of Natural Sciences, in Buenos Aires, while being funded by Argentinean government-sponsored doctoral fellowship.
Back into 2013, when I started my research, only 18 species were known in Mummuciidae. While conducting my research, I borrowed solifuge specimens from 27 museums and institutions from all around the world. This was only possible thanks to the institutional support that museums offer to scientific projects. Whilst the whole previous knowledge about Mummuciidae had been built on a handful of specimens (less than a hundred) (e.g., Roewer 1934), use of resources from all the collaborating institutions allowed me to gather over 6000 specimens belonging to this family, making this study the largest ever conducted on any group of solifuges. Likewise, field work conducted in Argentina, Chile, Brazil, Ecuador and Peru, contributed additional specimens and data.
Results were remarkable, although not necessarily unexpected considering the amount of material available and the scarce knowledge about this family. For instance, 40 new species were discovered, tripling the known diversity of the family. Of these, five new species have already been described and published in scientific journals (Botero-Trujillo 2016; Botero-Trujillo et al. 2017), whereas all others are currently in process of description and are expected to be formally named in the course of the next year.
My work with Mummuciidae would not have been possible without natural history museums. The current epoch we live in, with rapid industrial development and a growing human population, is accelerating the rate of species extinctions, by destroying habitats and causing global climate change. All of what is known about the diversity of Mummuciidae, including the recent discoveries here highlighted, have only been possible thanks to the biological collections and scientific museums around the globe. Museums serve as the pillar of a large inter-institutional and interdisciplinary network, connecting researchers from every country. They are also guardians and reservoirs of the planet’s past and present biodiversity. The existence of biological collections makes it possible that specimens and many other kinds of data sources will be available for study for many years to come.
Unfortunately, natural history collections are not indestructible, and at the beginning of September, a fire destroyed the collections of the Brazilian National Museum in Rio de Janeiro (see Greshko 2018). That terrible fire, destroyed millions of irreplaceable artifacts and animal specimens, including numerous type specimens. Type specimens are individuals to which the identity of the species is tied upon discovery, which makes them the reference specimen for the recognition of the species. Among the types destroyed in the fire at the Brazilian National Museum were specimens of two species of Mummuciidae: Mummucina exlineae and Cordobulgida bruchi. Sadly, Mummucina exlineae, was only known from the single type specimen housed at the Brazilian National Museum, so now, no other material of this species exists in the world and the only knowledge of these species exists in the form of publications and photographs. During my Ph.D., I was able to borrow the type material of these two mummuciid species and examine them only a few months before the fire occurred.
Museums and biological collections need to be taken care of. Their importance does not lie only in the exhibitions open to the public, but is limitless, on account of all the new information that is associated with the specimens stored in the collections. Several discoveries and contributions to science that collections can contribute will require many decades of work, and therefore, many decades are worth dedicating efforts to protect them.
About the author
Ricardo Botero-Trujillo completed his Biology B.S. at Javeriana University in Bogotá, Colombia. After a five-year period working in the pharmaceutical industry, Ricardo moved to Argentina where he earned a Ph.D. in Biological Sciences from the Universidad de Buenos Aires. His research mainly focusses on the systematics, taxonomy, and evolution of three arachnid groups: scorpions, solifuges and ricinuleids. Since 2006, he has described several new species of these three groups from different South and Central American countries. Ricardo joined the Division of Invertebrate Zoology at the American Museum of Natural History with a Theodore Roosevelt Postdoctoral Research Fellowship from the Richard Gilder Graduate School at the AMNH in August 2018. His current research covers aspects of Ricinulei evolution.
All photos taken by the author in the context of his doctoral thesis (Botero-Trujillo 2018).
Bird, T.L., R. Wharton & L. Prendini. 2015. Cheliceral morphology in Solifugae (Arachnida): primary homology, terminology and character survey. Bulletin of the American Museum of Natural History, 394, 355 pp.
Botero-Trujillo, R. 2016. The smallest known solifuge: Vempironiella aguilari, new genus and species of sun-spider (Solifugae: Mummuciidae) from the coastal desert of Peru. Journal of Arachnology, 44, 218–226.
Botero-Trujillo, R. 2018. Revisión Sistemática y Filogenia de los Solífugos de la Familia Mummuciidae (Arachnida, Solifugae). PhD Thesis. Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Argentina. Volumes I and II: 336 pp. + 209 pp. [unpublished].
Botero-Trujillo, R., R. Ott & L.S. Carvalho. 2017. Systematic revision and phylogeny of the South American sun-spider genus Gaucha Mello-Leitão (Solifugae: Mummuciidae), with description of four new species and two new generic synonymies. Arthropod Systematics & Phylogeny 75: 3–44.
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