Spiders, wasps and mice: keeping critters out of your telescope and observatory

Every observer has a story: the spider that abseiled across the view of Saturn, or the telescope case opened after winter to find the foam shredded into a mouse nest. Astronomy happens outdoors at night, with gear stored in sheds and garages, so we share the hobby with plenty of other creatures. Most are harmless, but a few can damage optics, chew cables or make an observatory a risky place to work. Here is what you are likely to meet in New Zealand and how to keep it out of your gear.

Spiders: the most common lodgers

An open Newtonian tube is a dark, sheltered tunnel with insects drifting past the front, which is prime real estate for a web-builder. Dew shields, finder scopes and the gap behind a focuser get the same treatment.

The usual suspects around New Zealand homes are the grey and black house spiders, which build messy, lacy webs in corners and window frames, the long-legged daddy long-legs, and the white-tailed spider, which does not build a catching web but wanders at night hunting other spiders and likes to shelter in folded fabric. That last habit matters if you leave a telescope cover or a blanket bunched up in the shed.

A little silk on a secondary mirror will not ruin a view, but webs collect dust and debris, and spider droppings left for months can mark a coating. To keep them out:

Cap both ends. Front cap on the tube, a cap or plug in the focuser, caps on the finder. A shower cap over the open end of a Dobsonian is a cheap, effective fix.
Check with a torch first. A quick sweep down the tube and dew shield takes ten seconds.
Remove webs gently. A rubber blower bulb or a soft brush on the tube walls is enough. Do not wipe the mirror or corrector to get silk off; leave optical cleaning until it is really needed.
Shake out covers before you put them on or take them off, and keep them hanging rather than folded on the floor.

Moths, beetles and the red torch question

On a warm, still summer night, any light you bring outside gathers a crowd: moths, midges and the occasional huhu beetle crashing into things, all ending up on eyepieces, in the tube and on your laptop screen.

The colour of the light makes a real difference. Many night-flying insects are most strongly attracted to ultraviolet and blue-rich light, which is why a cool-white LED floodlight can be a blizzard of moths while a warm amber one nearby is quiet. Deep red and amber light draw far fewer insects. Handily, red is also what we use to protect dark adaptation. A dim red torch, warm amber lighting around the observatory and no white work light left on while the roof is open will cut the insect traffic noticeably. Our post on outdoor lighting and the night sky covers choosing warm, shielded fittings for the rest of the section.

Red light does not stop mosquitoes, which find you by breath and body heat, so repellent is still worth packing on humid nights.

Wasps: a late-summer hazard

New Zealand has some of the highest densities of German and common wasps in the world, according to the Department of Conservation, because there are no natural predators, the winters are mild and there is plenty of food. Numbers build through summer and peak in late summer and autumn, just as the long autumn nights start to draw observers outside again.

An observatory roof space, the cavity behind a dome's base ring or the dark space under a raised deck all make perfect nest sites. German and common wasp nests are usually about the size of a soccer ball, but in the warm, humid north some survive the winter and keep growing. DOC notes that the largest recorded wasp nest in the world was found at Waimauku, near Auckland, at 3.75 metres tall. Smaller paper wasps also build pear-sized nests under eaves and on sheltered beams.

Wasps mostly stop flying after dark, but a disturbed nest will still pour out. Rolling a roof back or rotating a dome can shake a nest you did not know was there, so watch for wasps using gaps on sunny afternoons. And DOC warns not to shine a torch into a nest, because wasps will fly up the beam. A wasp sting is painful for anyone and can cause a serious allergic reaction in some people.

Mice and rats: the cable chewers

Rodents are the pests most likely to cost you money. Their front teeth grow continuously, so they gnaw constantly, and cable sheathing, dew heater straps and foam case inserts are easy targets. Damaged 12 V or mains wiring in a timber building is also a fire risk.

The ship rat, the most common rat in New Zealand, is an agile climber and often ends up in roof spaces, while house mice will move into any dry shed or garage as the weather cools in autumn. A telescope case full of soft foam, left undisturbed on a shed shelf for a season, is an ideal place to raise a litter.

To keep them out:

Store cases off the floor and away from walls, ideally in a sealed plastic tub inside the shed rather than on an open shelf.
Seal gaps. A mouse can squeeze through a gap about the width of a pencil. Steel mesh, brush seals and a door sweep close most entry points, and cable entries should be sealed, not left as open holes.
Don't leave food. Snacks, bird seed and pet food in the shed bring rodents in.
Check cables before each session after gear has been stored.
Set traps in tunnels or boxes along walls if you see droppings.

Clean up droppings and nests with gloves on, and wet them first rather than sweeping them dry. Rat urine can carry leptospirosis, a bacterial infection that Healthify describes as the most common infectious disease caught in the workplace in New Zealand.

When it is beyond a DIY job

A large wasp nest in an observatory roof or under the floor, or rats running through a ceiling cavity full of wiring, are both common enough in Auckland, where the mild, humid climate lets some wasp nests survive the winter and rodents breed for much of the year. Treating a big nest in a confined space you have to climb into is risky, and finding where rats are getting into a roof takes experience. In those cases it is worth calling in a local service such as Pest Control Auckland, then sealing the building once it is clear so the problem does not come straight back.

A storage routine that covers everything

Defence against critters is mostly good storage against damp:

Let gear dry before capping it, then cap every opening.
Store it sealed. Eyepieces in closed cases with silica gel; tubes and mounts under fitted covers.
Keep the space dry. Spiders, mould and many insects like damp, still air, so a small dehumidifier helps, especially through a North Island autumn.
Seal the building. Mesh behind vents, brush seals on roof gaps and sealed cable entries. Our post on weatherproofing a backyard observatory goes into more detail.
Check before you open. A torch down the tube, a look at the case foam, a glance at the roof gaps for wasps.

Not every visitor is a pest. Wētā are native and harmless, best carried gently outside, and most spiders keep insects down. The aim is simply to keep them out of the optics and electrics, so the only thing crossing your field of view is a satellite.