27 Aug 2015

The Bugs are in the House

From Our Changing World, 9:34 pm on 27 August 2015

By Alison Ballance

Brightly-coloured three level bug hotel on a tree trunk. This Bug Hotel had a 'do not disturb' sign, but ironically all the surrounding trees had been cut down. Rob Cruikshank thought the Bug Hotel and its tree had been spared.

This Bug Hotel had a 'do not disturb' sign, but ironically all the surrounding trees had been cut down. Rob Cruikshank thought the Bug Hotel and its tree had been spared. Photo: RNZ / Alison Ballance

A year ago some little, brightly-coloured buildings appeared around the campus of Lincoln University. With names like the Bug Ale House and the Blue Lagoon Hotel, they are Bug Hotels, also called Insect Hotels. They were built by landscape architecture students, with advice from ecology students, and the idea is to encourage native biodiversity by giving creepy crawlies places to live and raise a family in.

“We call them Insect Hotels,” says Nathan Curtis, an ecology tutor at Lincoln Unviersity. “But we’re obviously looking for any little invertebrates … all sorts of things that might be helping the environment.” He also pointed out that the hotels might provide a safe refuge for lizards.

Twelve months on ‘Bug Bloke’ Rob Cruickshank, one of the masterminds behind the Bug Hotels, is curious to find out what has taken up residence. I joined Rob and Nathan on a demolition job to investigate, which raised an interesting dilemma: how do you judge whether your Bug Hotel is succeeding without destroying it?

The answer is that you can’t, so Rob and Nathan opted to closely investigate just two of the Bug Hotels that had already been condemned because of tree felling in the immediate area, in one case, and building work in the other case.

The first Bug Hotel they autopsied was a small multi-coloured, multi-storey affair that had been in a copse of vegetation by the side of the road. The second one was a letterbox-based design that had been in a shrubbery next to a path. Both hotels used a range of materials to try and attract a variety of invertebrates, including dried grass, sphagnum moss, pine needles, old toilet roll tubes, corrugated cardboard, bits of bamboo, lengths of wood with holes drilled along their length, pine cones and a wide variety of other materials. Rob noted that among the features that make an effective Bug Hotel are the use of mesh across the front and back to prevent all this small material from spilling out.

“Lots of insects are thigmotactic,” says Rob. “They like to crawl into narrow spaces between things and feel their body pushed against the side of the place they’re hiding away in.”

Some hotels are made of untreated timber, and the idea is that these will slowly rot into the surrounding environment, providing home to different kinds of creatures over time, including wood-boring beetles. Other hotels are painted, to keep them weather-tight. Yellow, blue and white colours were chosen as they have been shown to attract different kinds of insects.

We were searching the Bug Hotels in the middle of winter, when there is less invertebrate activity, and there was only a small amount of evidence that the Bug Hotels had been used by insects such as weevils. The most common critters collected were spiders; “it was about six spiders to one insect,” noted Nathan.

While the number of residents was low, Rob pointed out that the hotels were not just for insects, but were there for people as well.

“The Bug Hotels are there to draw people in, give them something to look at, and help them think about the value of biodiversity.”

Rob Cruikshank (left) and Nathan Curtis (right) looking for invertebrates in amongst the different materials used in the bug hotel.

Rob Cruikshank (left) and Nathan Curtis (right) looking for invertebrates in amongst the different materials used in the bug hotel. Photo: RNZ / Alison Ballance

In a recent Our Changing World story on spiders, Cor Vink from Canterbury Museum showed me how most of the spiders around our houses are introduced species. Since the idea of the Bug Hotels is to encourage native biodiversity, Rob and Nathan were keen to find out if the spiders taking up residence in the Bug Hotels were native or introduced. I delivered the eight spiders found in the two hotels to Cor Vink at the museum, and he identified them as being two native species, two endemic species, one introduced species and three indeterminate (they weren’t mature so it was not possible to identify them). And, since spiders were the most abundant resident in the two Bug Hotels sampled, Cor agreed with me that perhaps they should be renamed Spider Hotels.

Spider ID

New Zealand has about 2000 species of spiders. There are about 70 introduced spiders in New Zealand, and they are mostly found in highly modified habitats. Here is a list of the spiders found in the Bug Hotels:

Garden orbweb spider (Eriophora pustulosa): the most common orb web species in New Zealand. It is a native species that was originally from Australia and arrived in New Zealand by ballooning, using silk threads to float with the wind. It’s called pustulosa because it has five pustules or knobs at the end of its abdomen. As its name suggests, it builds a web, and also builds a messy grey-green egg sac to lay its eggs in.

Australian ground spider (Nyssus coloripes): was probably introduced to New Zealand by people in the 1940s. They are hunters that don’t build a web and are very common around houses as well as in native habitat. They have orange front legs and white spots on their back and back legs.

Cobweb spider (Cryptachaea veruculata): is native to New Zealand and Australia, and common around bush edges and in gardens.

Square-ended cobweb spider (Episinus antipodianus): an endemic species in the family Theridiidae. It hangs upside down on a few threads of silk and catches prey from this position.

Square-ended crab spider (Sidymella spp): are ambush predators rather than web builders and lie in wait for their prey. Cor wasn’t entirely sure what species this was at first glance, but highly likely to be endemic (although there are several introduced species).

Ground spider (Scotophaeus pretiosus): Cor said that we have a number of endemic species, but we don’t know the status of this one. It’s thought to be introduced as it has no close relatives in New Zealand, however it’s also not been found anywhere else.

There were also two native jumping spiders, but as both were immature Cor wasn’t able to identify them – identification of spiders is often based on the genitalia of adult males. There are about 200 species of jumping spider in New Zealand, but although they’re a well-known group only about 50 are described, and Cor says you’d only be able to identify about 12 species based on the descriptions.