They’re Coming

Just when you thought you had enough to worry about with the effect of climate change on the environment, here’s something that’s bound to give you nightmares.

If you are like me and think spiders are already big enough and scary enough, then you’d better brace yourself. They are getting even bigger.

In Australia, where I live, we have some of the biggest and nastiest critters imaginable. For example we are home to the world’s most poisonous snake, the inland Taipan. Luckily it lives far, far, away from civilisation. Its venom is so toxic, it makes a death adder look like a wimp in comparison.

So the idea that our spiders might be growing even bigger is not exactly good news. Apparently this trend is happening the world over.

The cause of this has something to do with our cities becoming busier and more populated. Researchers have been examining how your everyday garden spider, like the harmless Golden Orb Weaver, is suddenly growing exponentially.

One species of this type of spider has been gaining weight almost at the same time as the city grows. Researchers say the further they are away from bush land and the more concrete there is with a corresponding reduction in leaf litter, the bigger the spider. And we are talking significant weight gain. For example, spiders found in a park away from the city had an average mass of 0.5 grams. But those in an inner city park averaged 1.6 grams or three times the size. Eeek.

Scientists are calling it the urban heat island effect and prey availability. Spiders are very sensitive to temperature. If it’s warmer they grow bigger. And urbanization has been a big benefit. The food or prey the spider eats tend to do well in small fragments of bush land like urban parks. And they do even better if there is lighting at night. So the spiders have more to eat so they can put more energy into growing bigger.

Income also plays a big part. Scientists found that wealthier areas in the city tend to have the largest spiders. The reason for this is less clear. But it might be because they have more parks and more concrete that heats up readily. Now the really bad news is that the trend is across the board. So poisonous spiders like the Australian Redback are also growing bigger. Global warming will encourage spiders to get bigger but they don’t like the really, really hot weather.

All of this has been pretty surprising to the scientific community. They expected that the opposite would be true. An increase in heat usually means an increase in the rate of development. It also means metabolic function speeds up so they mature early at a smaller size. But that is not what is happening.

The scientists do say the relationship between heat and body size is complicated. The heat might be allowing the spiders to hatch earlier giving them a longer growing season.

In any case, a healthy spider population apparently should be celebrated. They eat pests and provide food for birds. Spiders in urban areas should be encouraged. Sure. Anywhere except my backyard.

 

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