Poison applies to plants, animals, and fungi. It involves the transmission of toxins through contact and ingestion (eating something). Venom usually applies only to animals that forcibly inject toxins with stingers, fangs, etc. One of the most common misconceptions we hear at Hidden Pond is that some snakes are poisonous. They’re not. You could eat a venomous snake and be ok, but eating a poisonous mushroom would be a different story!

Most invasive species found in Fairfax County are plants. Here are a few that have great impact.
  Purple Loosestrife  - A wetland plant that, sadly, is sold at many area nurseries as a butterfly attractant. It crowds native wetland species.
  Garlic Mustard - This invasive not only competes with native plants, its roots change the chemical composition of soils. That kills or weakens native species.
  Oriental Bittersweet - A vine that chokes young trees and overtakes the crown of mature trees. It outcompetes trees for sunlight.
  Multiflora Rose - Competes and crowds the forest understory shrub species.

There are others. Invasive animals in Fairfax County include the Chinese Mantis, Red Eared Sliders, and European Starlings.

Most species rebounded after the area became parkland. Some fish species have declined or vanished from county waterways because of increased water temperatures due to development in areas adjacent to parks. Heavy siltation from development changed the gradient of stream beds. Illegal collecting of wildlife, such as reptiles and amphibians, has hurt some populations in county parks. Some of the decline could be attributed to pollution. Fish species that have declined or are now extirpated (extinct in this area) include Greenside Darters, Fantail Darters, and Pearl Dace.

Hidden Pond is home to many mammal, bird, reptile, amphibian, fish, and arthropod species. They include: 
  Amphibians: American toad, bullfrog, Cope’s gray tree frog, Fowler’s toad, gray tree frog, green frog, green tree frog, marbled salamander, Northern dusky salamander, Northern cricket frog, Northern red salamander, Northern two-lined salamander, pickerel frog, red-spotted newt, Southern leopard frog, spring peeper, white-spotted slimy salamander, spotted salamander, and wood frog.
  Birds: Northern cardinals, house finches, blue jays, several species of woodpecker, Carolina chickadees, barn owls, and mourning doves.
  Reptiles: Garter snakes, black rat snakes, Northern water snakes, ring-neck snakes, worm snakes, brown snakes, Eastern five-lined skinks, box turtles, painted turtles, snapping turtles, stinkpot turtles, and red-eared sliders. 
  Mammals: Flying squirrels, Eastern gray squirrels, striped skunks, red foxes, raccoons, white-tailed deer, Eastern chipmunks, various species of bat (such as the little brown bat), and occasionally coyote and even bobcat (very rare).  
  Fish: Bluegill, mosquito fish, black nose dace, creek chubs, tessellated darters, catfish (such as bullhead and madtoms), and American eels. 
  Arthropods: Many species of dragonfly and damselfly, crane flies, patent leather beetles, red-kneed millipedes, and nursery web fishing spiders.

The park can be considered one large ecosystem, and there are many predator-prey relationships and food chains here. Some animals may be at the top of their food chain in their preferred habitat, such as adult snapping turtles in ponds, but may rarely be preyed upon on land by medium-sized mammals, such as raccoons and foxes. Each animal and organism plays a part in the food chain. For example, mosquitos will lay eggs in slow-moving water, such as ponds, where they are eaten by mosquito fish, which may be eaten by a bluegill, which can be preyed upon by turtles, such as painted and snappers, or by water snakes. These animals may in turn by eaten by large predators, such as great blue herons. The smaller animals also depend on vegetation, such as duckweed, for concealment or else they would be easy meals. If you find an organism in the park, chances are there is another organism that depends on it for something.

People feed the animals, which is usually discouraged, and can disrupt habitats, whether intentionally or unintentionally. Seeds from invasive plants stick to shoes and clothing, and when people walk along trails they spread those seeds to new areas. Duckweed, an aquatic plant that floats on the surface of slow-moving or stagnant water, has skyrocketed in the pond because of fertilizer runoff from surrounding neighborhoods. The intense algae bloom often covers the entire surface of the pond. This provides shelter for some animals, but underwater plants can no longer get sunlight. The plants often die, causing a dangerous drop in oxygen levels in the water, and that can be lethal for fish. Some people have, unfortunately, taken animals from the park, which is illegal. There were bass in the pond but, to staff’s knowledge, they have been fished out. There have been several incidents of people taking turtles from the pond. Some people have introduced non-native pet turtles, such as red-eared sliders, that they think are native to the area but that are damaging to the pond ecosystem and to native turtles. Sadly, some people harm or even kill native animals in the park. In 2015, staff found a water snake that had obvious blunt force trauma to the head. Water snakes commonly get confused with venomous copperheads and cottonmouths (a non-native snake). Snakes are probably the most misunderstood animals in any ecosystem. Finally, wildlife diseases such as ranavirus, which affects local reptiles and amphibians, can be introduced either directly by people (often through their shoes) or by the release of an infected animal into the park. Luckily, Hidden Pond has not had too many issues with this.

Most of the park’s animals, except migratory birds, are here year-round. They have many interactions with people. We discourage people from feeding animals, such as waterfowl, as the wildlife may become dependent on people for food, a process called habituation. Animals can respond aggressively if they expect food and aren't fed. Frequent exposure to people sometimes causes animals to gradually lose their fear of humans. You can debate whether that is a good or bad thing.

Feel free to contact us. Visitor center hours are 9 a.m. to 5 p.m. Monday through Friday (closed on Tuesdays) and noon to 5 p.m. on weekends. We love visitors and can answer questions over the phone. You can also submit questions through Ask A Naturalist on the website. Animals on display at the visitor center, except for the diamondback terrapin, are native to Fairfax County and are in the park. There also are field guides for sale in the center. Come on in and say hello!