(Care2) - Humans have sprayed all sorts of pesticides to protect their crops since 2000 BC. Yet, after the Second World War, their use increased 50-fold. With so many chemicals left over, manufacturers decided to take the poisons meant to demolish and injure humans, and wage an eternal war against bugs instead.

These chemicals were inexpensive, effective, and enormously popular. For instance, when DDT was discovered as an effective insecticide, it was welcomed and even embraced as a solution against malaria and typhus. While making the bee documentary Vanishing of the Bees, I found footage of chemical trucks rolling through the streets engulfing people with clouds of the stuff. Their logo was even “DDT is Good for Me.” Meanwhile, one farmer in Utah I interviewed recalled how in the ’50s, he and his brother used to playfully chase each other in the fields with hoses that gushed chemicals.

With Rachel Carson’s Silent Spring, came the realization that poisons were harming our environment as well as our farmworkers. Typically pesticides were sprayed topically over crops. Systemic pesticides were introduced with the idea that they would cause less toxicity to humans as well as birds and mammals compared to the previously used organophosphate and carbamate insecticides.

The unintended consequences however have been incredibly alarming and have decimated bee populations all over the world. Here are 5 things you should know about these insidious chemicals.

Extremely Persistent

Systemic pesticides are highly water soluble and mobile, which means they can be applied in a number of ways: by drenching the soil; injecting them directly into trees; and even applying them as a seed coating. What is novel here is that the plant actually absorbs these chemicals and circulates it through its tissues. Unlike “traditional’ pesticides,” you cannot wash off systemic pesticides.