The sea wasp box jellyfish is perhaps the most deadly variety. This translucent sea-dweller may not look all that menacing, but it is the most venomous animal on planet Earth. Box jellyfish are deadly to many different animals, not the least of all, us. If you get stung by one of these animals, you are very likely to die.
Earth and Mars Conjunction: On the opposite end of the scale, Mars and Earth can be 401 million km apart (249 million miles) when they are in opposition and both are at aphelion. The average distance between the two is 225 million km. When Mars and Earth are at their closest, you have your launch window.
The average distance between the two is 225 million km (140 million miles). We figure that any trip to mars would be undertaken at a point when the two were closest, so we've used that distance to make our calculations! If you could walk from Earth to Mars at a brisk rate of 4mph would take about 4000 years!