Animal architecture reflects the biology of its builder. Three broad categories of animal constructions have been recognized: homes, traps and displays (Hansell 2005; 2007). Homes or shelters protect their builders from external physical and possible biological hostilities. They provide protection by means of their architecture, effecting avoidance of detection and the prevention of invasion after detection has occurred (Hansell 2005).

In architecture birds, spiders, termites, ants, bees and wasps are prodigies. Beetles exhibit the most numerous radiation within the animalia, but there are very few architects amongst them. In leaf beetles (Chrysomelidae) (about 50, 000 species) larval defensive structures, built of faeces and exuvial skin, are known (Chaboo et al. 2007, Chaboo et al. 2008, Prathapan and Chaboo 2011). Larvae of several leaf beetles are known to use faeces for defense, and nearly 20% of the described chrysomelid species have a form of faecal covering or faeces-associated structure at some point in their lifecycle (Vencl et al. 1999; Weiss 2006).

Two genera in the Cassidinae, namely Imatidium Fabricius (Gilbert et al. 2001) and Leptispa Baly (Maulik 1919; Voronova and Zaitsev 1982; Prathapan et al. 2009), have the only leaf beetles known to build leaf shelters. Larvae of nearly all of about 4500 species of Camptosomata (Cryptocephalinae and Lamprosomatinae) build cases from their own faeces (Chaboo et al. 2008).

Builders invest considerable resources and time making constructions. Hence, natural selection favours building behaviour which reduces the cost of building, whilst maximizing the benefits it offers. Nesting in existing cavities produced by primary cavity nesters, as in woodpeckers, is a common method of cost reduction used by birds. Low cost shelters of Leptispa pygmaea Baly larvae are formed by feeding alone—no cutting, bending or secretion of silk or glue is required (Prathapan et al. 2009). A type of low cost shelter, named a leaf-hole shelter, is here reported for the first time for two species of Orthaltica Crotch, a genus of minute leaf beetles (Figs 1, 4–8).

The genus Orthaltica is distributed in the Afrotropical, Australian, Nearctic and Oriental Regions (Seeno and Wilcox 1982; Reid 1990) and contains 44 named species, of which the majority (32 species) are distributed in the Oriental Region. The taxonomy of Orthaltica is complex, currently including eight generic synonyms. Crioceris copalina (F.), the type species, occurs in the Nearctic Region. In India the genus is represented by at least ten species level taxa, of which only six have been formally named and described: Orthaltica assamensis (Scherer, 1971), Orthaltica bengalensis (Basu & Sengupta, 1978), Orthaltica coomani (Laboissiére, 1933 in Basu and Sengupta 1978), Orthaltica dakshina (Basu & Sengupta, 1978), Orthaltica minuta indica (Medvedev, 1998) and Orthaltica purba (Basu & Sengupta, 1985). We here describe two species that utilise leaf-hole shelters. However, a revisionary study of the genus is necessary, at least in Asia, to clarify both species boundaries and the relationships between species groups currently placed in Orthaltica.

Five species of Orthaltica were collected from various localities in southern India, along with their host plants, forming part of our long term study of the leaf beetles of India. Species from this genus are known to feed on plants from the Combretaceae, Melastomataceae and Myrtaceae. Leaf-hole sheltering, described below, was observed in two species feeding on Syzygium (Myrtaceae) and Terminalia (Combretaceae) species respectively. The Orthaltica species feeding on Syzygium (Gaertn.) is here described as Orthaltica syzygium new species, and the species on Terminalia L. as Orthaltica terminalia new species. Orthaltica syzygium was collected from various localities in the states of Karnataka (Kottigehara, Kudremukha) and Kerala (Arippa, Kumarakom, Vattavada) on Syzygium cumini (L.) Skeels, Syzygium caryophyllatum Alston and Syzygium travancoricum Gamble. Orthalitca terminalia was also collected in the states of Karnataka (Kudremukha) and Kerala (Calicut University Campus, Kallar, Trichur), but on Terminalia cuneata Roth and Terminalia paniculata Roth. The leaf-hole shelters on Terminalia paniculata were initially formed by a Tricliona sp. (Eumolpinae). Natural populations of all the Orthaltica species were carefully observed in the field for feeding and shelter seeking behaviour. Leaf-hole shelters of Orthaltica syzygium were observed at the Kudremukha National Park on Syzygium caryophyllatum, but were initially formed by a Basilepta sp. (Eumolpinae) (Fig. 3). Other leaf feeding beetles, but particularly Eumolpinae, were observed for their feeding activity on the hosts of Orthaltica. Artificial leaf holes were presented to the beetles on leaf laminae of Syzygium travancoricum. Holes were made with a punch, generally used for making the card points on which small leaf beetles are mounted. The punch created elongate, triangular holes of 7 mm in length and a width of 2 mm at the base. About 60 leaves were provided to adults of Orthaltica syzygium on 20^th April, 2013, each with six holes punched on the lamina. Occupation of the holes by these beetles was observed on 20^th May, 2013 and 20^th August, 2013 and could easily be determined by checking for the presence or absence of feeding trenches radiating from the hole (Fig. 6).

Descriptive terminology follows Konstantinov (1998). Holotypes of the new species are deposited in the National Museum of Natural History, Smithsonian Institution, Washington, DC, USA (USNM). Paratypes will be deposited in the National Pusa Collection, Indian Agricultural Research Institute, New Delhi, India (NPC); University of Agricultural Sciences, Bangalore, India (UASB); Natural History Museum, London, United Kingdom (BMNH); and in the personal collection of the first author (PKDC). Plant vouchers with accession numbers are deposited in the Calicut University Herbarium, Calicut, India. Different labels on specimens are denoted by numbers and separated by “;”.

Besides Orthaltica, species of Terminalia and Syzygium also support other leaf feeding beetles belonging to the family Chrysomelidae, as well as to the family Curculionidae. These beetles, being much larger (length 2.2 – 4.5 mm) than Orthaltica (length 1.2 – 1.6 mm), feed by cutting holes in the laminae. The adults of Orthaltica are extremely small and incapable of cutting holes in the laminae, but rather produce elongate feeding trenches on their adaxial surface. Adults of Orthaltica syzygium and Orthaltica terminalia utilise holes previously made by larger herbivores, in the leaves of their respective hosts, as shelter. They then create feeding trenches which radiate from the leaf hole which is their shelter (Fig. 1). Beetles could be seen inside holes during most of the day when they were not feeding. They came out of their leaf-hole shelters to feed, forming irregular trenches radiating from the hole. When threatened by means of a finger or a stick, beetles in holes immediately shifted their position to the reverse side of laminae, thus making themselves invisible to the enemy on the opposite side. It was observed that whenever an ant appeared on one side of the lamina, the occupant of a leaf-hole shelter also shifted its position to the reverse side.

Leaf beetles of the subfamily Eumolpinae are the most common primary hole makers on Syzygium and Terminalia species. At Kudremukha National Park it was observed that a Basilepta sp. (Eumolpinae) leaf beetle chewed holes in the laminae of Syzygium caryophyllatum (Fig. 3). Orthaltica syzygium released on the leaf readily occupied the leaf-hole as a shelter (Fig. 4). By the second day feeding trenches were observed radiating from the leaf-hole shelter (Fig. 5).

The triangular artificial holes, made in the laminae of Syzygium travancoricum with a punch, were accepted as shelters (Fig. 6). It was observed that the shape and size of the holes were not exactly what the beetles required. Holes were then resized by partitioning—walls were constructed using faecal pellets (Fig. 7). A single occupant was observed in a hole in most cases. However, when high population densities occurred, several beetles could be seen in a single hole that was large enough to accommodate them (Figs 1, 8).

In the case of the triangular artificial leaf-holes, beetles had a distinct preference for the narrow vertex of the triangle, above its wider base (Fig. 7). This may be because their size allowed them to easily fit inside the narrow apical angle. On 20^th May it was found that, of the 316 triangular holes examined on 53 leaves after a month, 235 were occupied. Similarly on 20th August, after a period of four months, of the 319 triangular holes on 58 leaves, 240 were occupied.

Even when suitable leaf-holes were available on leaf laminae, non-shelter forming species never occupied such holes (Fig. 2). Orthaltica syzygium confined on leaves without holes fed normally on the adaxial surface of the laminae.

Leaf-hole shelters provide a roosting site that offers a certain degree of camouflage as well as protection. In the field it was observed that on sensing the presence of an enemy on one side of the leaf the occupant of a leaf-hole shelter could easily shift to the other side, making itself invisible to the intruder. It may also be presumed that larger predators cannot pass through the hole in pursuit of the occupant. The leaf-hole, as well as the surrounding area with feeding trenches, turn dark brown and provide a dark background from which the beetle cannot be easily differentiated by a potential predator. On the other hand, the leaf-hole shelter can also provide sufficient cues for a specialist enemy that only needs to learn to locate the leaf-hole shelter to get the inmate. This is the case where insect collectors are concerned—it is easy for them to locate leaf-hole shelter and collect the beetles utilising them.

Leaf-hole shelters were observed in two of the five Orthaltica species found in southern India. This is certainly a behavioural novelty of evolutionary significance. It can be seen as an example of Lorenz’s (1937) discovery that a behaviour pattern can be treated as an anatomical organ, which Dawkins (1982) further synthesized and developed into the hypothesis of “the extended phenotype”. It is likely that this extracorporeal adaptation evolved in two lineages of Orthaltica in response to interactions with other leaf feeding beetles. Further investigation into the prevalence and diversity of herbivorous beetles on the host plants of Orthaltica, and their interactions with each other, might provide the answer.

Adult chrysomelids, unlike their larvae, never carry their faeces in the form of defensive shields. However, females of many species are known to defecate on their eggs after oviposition. Adults are also known to defecate when seized (Müller and Hilker 2004). The use of excreta for the construction of defensive structures or retreats was, until now, not known for adult leaf beetles.