Pests commonly found in Phoenix, Arizona

Scorpions

Every scorpion in Arizona glows blue-green under ultraviolet light, which is how a night inspection works, but only one of them is a real medical concern.

Where you find one matters more than that you found one. A scorpion in the yard at night is ordinary, because the desert is full of them. A scorpion indoors means there is a route in, and routes in are physical problems rather than chemical ones.

They do not need a hole. A bark scorpion climbs, and it passes through gaps most people would never think to seal: the weep screed along the base of a stucco wall, a garage door seal that has hardened and lifted at the corners, the point where a patio roof meets the fascia, block wall weep holes, gaps around pipe and conduit penetrations, and the underside of a poorly fitting exterior door. Because this is the one that climbs, a roofline gap or an upstairs window is as usable an entrance as a doorstep.

Outside, they shelter under anything flat that sits on the ground and stays cool: pavers, flagstone, stacked timber or brick, pool equipment, bags of soil, decorative rock. Block walls are close to ideal, because the cavities hold cool air and moisture and connect one yard to the next.

Count rather than react. One sighting in July tells you very little on its own. Several found along the same wall on the same night tells you a population is living in the yard, and that indoor sightings will keep arriving until the yard and the perimeter change. That is why most of the useful work on a scorpion problem happens outdoors and is physical: sealing, weatherstripping, clearing harbourage and reducing what they are hunting, with treatment supporting that rather than replacing it.

The practical distinction is body shape. A bark scorpion looks slender and delicate; the two harmless ones look heavier and more robust. Size will not separate them either, and a small or pale one raises a different question — see baby scorpions in Arizona. If you are unsure, photograph it and ask — and for anything to do with a sting, Poison Control on 1-800-222-1222 is free and staffed around the clock. More on scorpion control.

Rodents

A rodent problem is a building problem before it is a pest problem, and the order matters: find the way in, close it, then deal with what is already inside. Trapping on its own empties an attic for a few weeks and then it refills.

The route is usually above head height. Roof rats climb, and Phoenix gives them ladders: mature trees touching the roof, palm skirts, oleander hedges, bougainvillea trained up a wall, and the pipes and conduits that run up the outside of a house. From the roof they take whatever is open, which is normally a lifted tile edge, an unscreened vent, a gap where the fascia meets the roof deck, or the chase around a plumbing stack. Mice come in lower, through the garage, weep holes and the gaps under doors.

What you hear narrows it before anyone goes into the attic. Scratching and running overhead after dark points upstairs. Noise inside walls at floor level or behind kitchen units points to mice. Movement that stops the instant you make a noise and starts again a minute later is a live animal rather than timber settling.

Outside, the attractants are usually obvious once they are pointed out: fallen citrus left on the ground, dog or bird food stored open in the garage, an uncovered compost heap, a leaking drip line or a pet water bowl, and dense ground cover that lets them travel without crossing open ground. Clearing those will not end an established infestation on its own, but leaving them guarantees the next one.

Spiders

Most spiders in a Phoenix house are harmless and are eating the insects you would rather not have. Two are worth knowing on sight, and one widespread belief is simply wrong.

The web tells you more than the spider does, and you will usually meet the web first. A widow web is not the neat wheel people picture. It is an untidy, three-dimensional tangle, noticeably strong, and it is almost always low down and somewhere that never gets brushed against: block wall weep holes, water meter and irrigation boxes, the underside of patio furniture and barbecue lids, the back corners of a garage, stacked pots, the space behind a bin. Clearing those sites properly, sacs included, is what spider control is mostly made of.

If you find the web but not the occupant, look for egg sacs, which are pale papery spheres suspended in the tangle. A web cleared with the sacs left behind is not a cleared problem.

Almost everything else in this group is doing you a favour. Crab spiders and wolf spiders hunt rather than trap, which is why you meet them walking across a wall or a floor instead of sitting in a web, and why they appear indoors on summer nights. Removing them one at a time achieves very little. What actually reduces spiders is reducing the insects they are eating and the clutter they shelter in, particularly anything stacked against an exterior wall.

A wolf spider is the one people most often get wrong. Two of its eight eyes are large and forward-facing and throw back a green shine in torchlight, which settles it in a second after dark. A female carries her egg sac attached behind her and later carries the spiderlings on her back, which is what makes a big one look so alarming. It is not a tarantula and it is not a recluse. If you need to settle which species you are actually looking at, our guide to spiders in Arizona covers identification down to the eye pattern.

The practical response to any of them is the same, and it is not spraying. Clear stored items off garage floors, keep firewood and boxes away from walls, shake out shoes and gloves that have been left outside, and wear gloves when you move anything that has sat undisturbed.

The ones that bite you

Bites are the least reliable evidence on this page. Reactions to the same insect vary enormously between people in the same house, some people show nothing at all, and several unrelated things produce marks that look alike. Treat bites as a reason to go looking for physical evidence, not as the identification itself.

Where and when does narrow it. Bed bug bites appear on skin left uncovered in bed and are noticed on waking, and what confirms it is not on you but on the bed: dark specks along a mattress seam or piping, in the seam of a headboard, or on the underside of a slat. There is more on verifying and treating them on the bed bug control page. Mosquito bites happen while you are awake, outdoors or near an open door, and the Valley runs two patterns, the container breeders that bite low on ankles and legs in daylight and the ones that come at dusk and after dark. Kissing bugs feed at night and are drawn to lights, and they are tied to pack rat middens, so a yard with stick middens under a shed or around pool equipment already contains the explanation. With mosquitoes the useful detail is that the daytime biters do not travel far, so being bitten in your own yard in daylight means the water is almost certainly on your own property, and mosquito control starts with finding it.

For any bite that is spreading, unusually painful or making someone unwell, the right call is a doctor rather than a pest control company. Our part is finding and removing the source. What bit you becomes a medical question the moment it stops being an identification one. Bed bugs are the one group here where the biology does most of the explaining, and our guide to the bed bug life cycle sets out why they are so hard to shift. And if it is mosquitoes, the question is usually what to buy rather than what it is — our guide to mosquito repellents that actually work sorts the useful products from the rest.

The big ones that look dangerous and are not

These are the finds that produce a 2am phone call, and almost none of them deserve one. They are the largest invertebrates most Phoenix households will ever meet, they turn up suddenly after summer rain, and every one of them is harmless to people. Knowing them on sight saves a lot of alarm.

There is a pattern in this group worth remembering. In the Sonoran Desert, size is a poor guide to danger. The three-inch beetle is harmless and the two-inch scorpion is the one to take seriously.

Three of these are worth a little more detail, because they are the ones people search for by name and struggle to find.

The Jerusalem cricket answers to at least four names — child of the earth, potato bug, Jerusalem beetle — which is most of the reason it is so hard to look up. It is not a cricket and has nothing to do with Jerusalem. It lives underground eating roots, tubers and other insects, and surfaces when rain or irrigation softens the soil, or when someone turns a bed over. It drums its abdomen on the ground to find a mate, which is why people sometimes hear a faint tapping at night. It can pinch hard with its jaws if you pick it up, so do not, but that is the whole story. We have written it up properly in Jerusalem crickets in Arizona, including why nobody can agree where the name came from.

The palo verde beetle spends the interesting part of its life out of sight. The adult barely eats and lives only a few weeks, and its entire job is to mate. The grubs spend two to four years feeding on the roots of palo verde, olive, rose and other stressed trees, so a heavy emergence in your garden is telling you something about a tree rather than about your house.

The pinacate beetle’s headstand is a bluff worth knowing: the spray is foul and can sting the eyes, and that is the limit of it. Both it and the palo verde beetle sit in a wider group we have written up in Beetles in Arizona, along with the handful that are actually worth acting on. The centipede is the one real exception here — though the small, delicate, very long-legged house centipede you find in a bathroom is a different animal entirely, harmless, and a sign of damp rather than anything else.

How to photograph what you found

Almost everything above can be identified from a phone photograph if it is taken with a little care, and that saves you a visit.

Put something ordinary beside it for scale — a coin, a pen lid, a fingertip at a safe distance. Size settles more identifications than colour does, and it is the thing that is impossible to judge from a photo without it. Get the light from the side rather than straight on, so texture and markings show instead of washing out in the flash. Take one close shot and one wider shot showing where it was, because location is often as diagnostic as the insect: a drain, a mattress seam, a footing, a wall cavity.

If it is damage rather than a live pest, photograph the pattern — mud tubes on a footing, frass pellets on a sill, rub marks along a beam, gnawed fruit. And if it is dead and intact, keep it in a sealed bag or a jar. A specimen settles the question in seconds.

Identification questions