Mud-Wasp Nests and Rock Art

Rock Art Research 2014 - Volume 31, Number 2, pp. 225-231. R. G. BEDNARIK 225 KEYWORDS: Sphecidae – Thermoluminescence – Mud-wasp nest – Contact rock art MUD-WASP NESTS AND ROCK ART Robert G. Bednarik Abstract. The optically stimulated luminescence analysis of fossil and mineralised nests of mud-dauber wasps is examined and difficulties in the interpretation of results are considered. The utility of carbon isotope analysis of such features is advocated, and an example of its application to a Late Pleistocene specimen is reported. Also considered, through the example of a major Australian contact rock art site, are some difficulties in interpreting direct dating information pertaining to rock art. It is shown that organics in paint residues may be taphonomic features acquired over time, and that the time intervals between datable elements and physically relatable rock art may be of such great duration that such results are of limited practical value. Introduction nations of Roberts et al. are of particular importance. The pioneering study of Roberts et al. (1997) of- Roberts et al. (1997) provide data from two fossil fered a valuable tool for archaeological and palaeocli- wasp nests, one of which (KERC5) has yielded the matic research by demonstrating the potential of nests above date, but is in fact not associated with any rock of mud-dauber wasps for providing environmental art. Another, nearby nest (KERC4) ‘may be related to the and dating information. These authors hoped that the Bradshaw style’ (Roberts et al. 1997: 697), represented ‘worldwide distribution of mud-wasps’ would facili- only by an untypical pictogram, not a typical Gwion tate wide applicability of their technique, but in the figure. It yielded a wide range of palaeodoses, from 0.5 sixteen years since this potential has not been realised. Gy (Gray) to about 75 Gy. After discarding those grains The only factor of their report that has had wide reper- that were thought to have been exposed to ‘modern cussions is the proposition that one of their optically sunlight’, of the remaining 36 grains a mean age of 23.8 stimulated luminescence (OSL) determinations pro- ± 2.4 ka bp was proposed for 21 of them, and 16.4 ± 1.8 vides a minimum age of 17.5 ± 1.8 ka for an anthropo- ka bp for the remaining 15 grains. However, only a few morphous rock painting, which has given rise to many millimetres of the rim of this nest overlies the painting derivative claims. Significantly, this result is not only (Aubert 2012: Fig. 1), where it is less than 1 mm thick, at odds with alternative Holocene age estimates of the therefore only the ‘most recent’ of the grains (those Gwion rock art traditions in question (Watchman et al. discarded) are likely to relate to this paint residue. 1997), it is also the only ‘direct date’ (Bednarik 2002, No data were reported from grains overlying the 2010) from any Australian rock art suggesting the use pictogram, therefore no dating was achieved. It is well of iconic depiction in the Pleistocene. All other cases of known that mud-dauber wasps prefer to construct nests such age claims are based on the purported depiction on the remains or stumps of pre-existing nests, which of extinct animal species or their tracks, which are un- may account for the wide range of palaeodoses from testable propositions guided by the belief to be able to KERC4. Moreover, the grains most likely postdating discern those aspects of a motif that are naturalistically the painting are those discarded by Roberts et al. as depicted (Bednarik 2013). Therefore the OSL determi- being ‘contaminated’ (Fig. 1). In this determination they Figure 1. Schematic section of the lower edge of wasp nest KERC4 (after Roberts et al. 1997; Aubert 2012), showing that only the surface-nearest but discarded deposit postdates the paint residue. There is no stratigraphical or temporal relationship between the pictogram and the presumed two older cohorts of grains. 226 Rock Art Research 2014 - Volume 31, Number 2, pp. 225-231. R. G. BEDNARIK cules, phytoliths, carbon particles (charcoal), starch grains, and parts of graminae and di- cotyledons. Much of the organic component can be assumed to be of an age similar to that of the nest, yet its obvious potential to provide relevant carbon isotope age estima- Figure 2. (a) Black and yellow mud dauber (Sceliphron tions has not been exploited for the presumed caementarium); (b) collecting mud and (c) constructing nest. Pleistocene nests, except that Yoshida et al. (2003) reported a conventional (uncalibrated) ignore that all other grains in a wasp nest must also radiocarbon age of 26.3 ± 0.2 ka bp (OZE069) for pollen have been near the surface at some stage, and would grains of 5–10 μm diameter extracted from a mud-wasp then have been similarly affected by sunlight. Therefore nest unrelated to rock art. The same applies to the ter- their dates, if they are relevant, would have to be mite runways, which are even more common at rock art conservative minimum dates. Clearly, the taphonomic sites than mud nests (e.g. Brady et al. 2010), and which history of each nest, which is essentially unknown, consist essentially of soil, tiny rock fragments or grains needs to be taken into account in considering the OSL and digested wood. data secured from it, as is the case in concealment by other accretionary deposits (Liritzis et al. 2012). OSL analysis of mud-wasp nests Mud-dauber or potter wasps, of the families Sphe- ‘Thermoluminescence’ (TL) refers to the release of cidae and Eumenidae, can be divided into primary and energy by crystalline solids when heated or exposed secondary nest builders: those that construct new nests, to light (Kennedy and Knopf 1960; Aitken et al. 1968; and those that occupy abandoned nests of other species Fleming 1968; Fagg and Fleming 1970; Aitken 1990; and modify them by creating their own cells. Several Elias 2007). Ionising environmental alpha, beta and species have been reported to impact upon rock art by gamma radiation results in the release of electrons establishing nests in rockshelters, including Sceliphron and other charge carriers (‘holes’) in these materials. laetum, Sceliphron formosum, ?Pison sp., ?Abispa splendida, Electrons become trapped in defects of their crystal Paralastor alexandriae and ?Odynerus sp. (Naumann 1983; lattice, such as impurities or chemical substitutions. Naumann and Watson 1987) and Sceliphron caementa- These metastable charge carriers accumulate over time rium. Each of them builds distinctive structures from at a largely constant rate determined by the dose of the mud (Fig. 2), which under favourable conditions can radiation. They can be ejected from their ‘traps’ by an survive for many millennia because they tend to occur input of additional energy, which releases their excess in sheltered locations and they can become mineralised. energy as light, measurable in photons. This energy, the Although mud-dauber wasps are of wide distribution, TL, is therefore, with some qualifications, a function of their nests are particularly common in tropical or sub- the time since the material was last heated (e.g. ceramics tropical sandstone shelters. They share this trend with or heating stones) or exposed to light (e.g. crystalline termites (Isoptera), whose covered runways or galleries mineral grains). In using OSL analysis (Huntley et al. provide the same potential to assist in both dating and 1985; Wintle 1993; Aitken 1994; Duller 1996; Murray et palaeoenvironmental studies (Watson and Flood 1987), al. 1997) to estimate the antiquity of an ancient mud- although this has remained unexplored so far. wasp nest, an aliquot of quartz grains of the former mud The mud from which the nests of the mud daubers is extracted and the environmental radiation of the rock are made is gathered by the females along the margins is measured with a gamma spectrometer. The ‘trapped’ of ponds and streams, carried in their mandibles and energy is released by green/blue light (~500 nm) and is brought to protected sites. As each cell is completed it thought to represent the time since the grains were last is provisioned by Sceliphron caementarium with spiders, exposed to bright light. such as crab spiders, orb-weaver spiders and jumping However, there are numerous sources of impreci- spiders, still live but immobilised (Fig. 3). Each cell is sion or uncertainty, such as the variability of the en- sealed once an egg has been deposited, and the spiders vironmental dose rate (Dunnell and Feathers 1994) or serve as food for the developing larvae. Each wasp spe- the moisture content. In order to eliminate the need to cies prefers particular kinds and account for dose rate alpha and beta radiation (which sizes of spiders in stocking these is far more ionising than gamma radiation but has very larders, and there may be more limited power of penetration), the outermost 2 mm of than twenty spiders stored in one samples is usually removed in the case of TL analysis cell. The mud typically contains of pottery. But this may not be readily possible with grains of clay, silt and small sand the small deposits of mud-nest residues and has not fraction, organic ketones (prob- been attempted. Instead, individual grains of the fine Figure 3. Provision- ably of salival origin), as well as sand fraction (~100 μm) were etched with hydrofluoric ing mud dauber numerous incidental inclusions. acid to remove their outermost layers of 10–20 μm, the nest with immo- Among these have been reported presumed penetrating range of alpha particles (Rob- bilised spider. pollen grains, spores, sponge spi- erts et al. 2000). Disequilibrium in the U and Th decay Rock Art Research 2014 - Volume 31, Number 2, pp.

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