The only thing more alarming than the pests you can see are the ones you can't.

I am not at all squeamish when it comes to spiders, snakes, and most bugs, since I can see them. I appreciate their natural place in the world, and some are very beneficial to gardens. Then I married a veterinarian, and my view of the natural world took a darker turn. Microscopic organisms are an entirely different story. The only thing more alarming than the pests you can see are the ones you can't. Here's a countdown of the top 10 creepy crawlies you should know about.

10. Hookworm (Ancylostoma caninum and Ancylstoma brazilienese)

I ran barefoot through most of my childhood without contracting any parasites, something that surprises me now that I know what is lurking in the soil. Gardeners with dogs and cats need to be especially careful when it comes to working in the dirt with bare hands. Dog and cat poop can contain hookworms, which penetrate bare skin and cause unpleasant inflammation. Most of us already make an effort to prevent our pets from defecating in our gardens, so this is just one more reason to encourage them to do their business elsewhere.

9. Tetanus (Clostridium tetani)

Rusty nails aren’t the only things gardeners have to worry about. Clostridium tetani, the bacteria that causes tetanus, is widely distributed in soil and in the gastrointestinal tract of horses, sheep, cattle, dogs, cats, rats, guinea pigs, and chickens. Gardeners who use manure in their gardens are especially at risk. The good news about tetanus is that most adults in the U.S. are vaccinated. Now that I know just how prevalent tetanus is, I plan on making extra certain that I keep that vaccine up to date.

8. Roundworm (Toxocara canis)

Roundworm is a highly unpleasant infection that lurks in dog poop and occasionally cat poop, not to mention other species of animals. Humans can contract it by accidentally eating the eggs or roundworm, which hide out in the soil and enter our bodies when we neglect to wash our hands and scrub the dirt from beneath our fingernails. Luckily, washing our hands and peeling root vegetables usually prevents roundworms from gaining entry, and preventing animals from pooping in or near the garden also helps.

7. Giardia duodenalis

There is nothing pretty about Giardia. The parasite causes giardiasis, which is best known for its major symptom: diarrhea. Luckily for gardeners, it is most commonly contracted by drinking contaminated water, but it can be found in soil and on our crops if infected animals poop in the area. This is a good reason to be careful when irrigating with natural water sources like rivers, lakes, and ponds, as the parasite can attach itself to produce. Giardia gives us one more reason to wash produce and hands well before eating.

6. Toxoplasma gondii

The world is a litter box, according to cats, and that means that your garden is a perfect place for your own cat and neighborhood cats to deposit their business. Toxoplasma gondii is a single-celled parasite that causes the infection toxoplasmosis. The disease doesn’t cause many issues in healthy humans, but it is dangerous for pregnant women and individuals with compromised immune systems. The parasite has also been linked to mental health problems including schizophrenia and rage. The best way to avoid contracting this disease is to wash your hands after gardening and to abstain from snacking on vegetables in the field until after they have been thoroughly washed.

5. Cabillus cereus

Bacillus cereus gastroenteritis is an unpleasant bacterial infection caused by Bacillis cereus that affects an estimated 63,400 Americans annually. The bacteria live in decaying organic matter, in fresh and salt water, on plants, and in worms. They usually infect humans by entering food processing plants, but gardeners are at risk. Wearing gloves, washing food, and covering wounds and cuts can help prevent gardeners from contracting this and other bacterial infections.

4. E. coli

Some E. coli bacteria are perfectly harmless. Others cause infection. From a gardener’s perspective, the dangers of E. coli mostly have to do with manure and animal handling. Most gardeners I know are eager to scoop up free manure for their compost, and quite a few of my gardening friends (myself included) come in frequent contact with livestock. This puts us at an increased risk of exposure. Composting manure helps eliminate E. coli (although it is not a guarantee), which is why it is a good idea to avoid applying raw manure directly onto our gardens.

3. Velvet Ants

I said I wasn’t going to mention creepy crawlers, but this insect is too terrifying to overlook. These insects are not ants, but are actually a species of wingless wasp with a distinctive velvety appearance. I did not have these where I grew up, and I didn’t believe it when someone told me they were commonly called “Cow Killer Ants” because the sting of the female is so excruciatingly painful. They crawl along in lawns and gardens and are just one more reason why I no longer walk barefoot out of doors.

2. Ticks

Nobody likes ticks. When I grew up in Upstate New York, which was not that long ago, I didn’t even know what a tick was – we just didn’t have them. Now they are everywhere, and while ticks are creepy in their own right, it is the diseases they carry that are a gardener's biggest concern. There are too many to list, and though Lyme might be the most well known, it is certainly not the only disease we need to be aware of.

1. Mosquitoes

Irritating. Itchy. Dangerous. Mosquitos are more than just a nuisance; they are also a health risk. The Zika virus is the latest in mosquito-transmitted diseases, and it certainly won’t be the last. West Nile Virus, Dengue fever, Chikungunya, and malaria came before it and affect many parts of the world. The unfortunate truth is that sometimes bug spray isn’t enough, which is why mosquitos are number one on my list of terrifying things that lurk in our gardens.